Comparing differences betwee EA and EW rulesets? Well the Epic in Exodus Wars.pdf (linked in the post above) does a pretty good job of indicating the major differences/analogs though of course there's the assumption (explicitly stated in the document) that the reader is familiar with EA. But in a nutshell:
[wall o'text incoming!]
1. D10's vs D6. Important I feel as D10's are common and provide greater fidelity. Basically D6s probably should be used in board games, not wargaming at this level of detail. After years of "burn-in" with EA it's become apparent there's lots of little bits that would be nice to have some more granularity to represent them (one example I love is Assault Cannons which are too weak to properly represent their AP firepower in a D6). This is absolutely a math-weanie thing (which I am).
2. EA uses three types of attacks. AP (anti-personnel), AT (anti-tank), and then Macro Weapons (MW). AP can only put damage on INF targets, AT only on AV, and MW on either. MW prevent armour saves on the hit target unless it has RA (reinforced armour) and only then, a single save. On the surface that sounds great but there's lots of places that kinda turns out that were not a good idea in retrospect. MW are EQUALLY good at killing tanks as they are infantry. But what if you need/want to model a weapon that's an absolute tank killer when it hits, but only hits 1/3 shots but also needs to be rubbish at attacking inantry? Can't model that easily using MW (as it's equally good at both) and it should cut straight through most AVs (e.g. no save) but you need MW to represent that. No bueno...
3. EA is a rules system for a specific setting. EW is a rules system with a default setting. This means that terms generally are generic tactical terms/concepts and not actually tied to the setting names. Minor but handy to use in multiple settings without needing to jump through mental hoops.
EW instead keeps AP (P attacks) and AT (A attacks) rolls explicity listed and thus indpendent from each other ALWAYS. When you need to prevent aromour saves on a target (or only a single for really tough things) that concept is represented as a new ability called Anti-Armour which is applied on the weapon line itself (similar to how Disrupt or Indirect fire work in EA as an ability). By moving it from the TYPE of attack to a keyword ability ON the attack, we retain that fidelity and even better, doesn't require any special cases, unlike in EA. So the above hypothetical weapon example in EW would be "A(8+), Anti-Armour". That's it. Can't damage infantry, hits around 30% of the time, and prevents armour saves unless on Robust targets (the Reinforced Armour analog).
4. In EA each hit causes only a single point of damage on a failed save. For a weapon that's especially powerful, it can be reprsented as MW, with all the drawback as I noted in #2 attached. However "regular" MW hits still only do a single point of damage. So there's a fringe exception for the exception for an attack type (so if you're keeping count here boys and girls, that's now 4 types of attacks) and that's called Titan Killer (TK). A TK weapon works the same as MW except it can cause more than a single point of damage on a hit (in example, TK(2) causes two damage on each hit and TK(D3) would cause 1-3 points randomly on each hit). Oh as TK is MW ++, it suffers on all the same problems as #2. Fine and good but what happens when you need to represent a weapon that's a "regular" weapon but one that is especially good at destroying armour if it penetrates but shouldn't have a super high chance of penetration (basically the US Army WW2 bazooka)? Well that's EXACTLY the the difficulty when you try and model something like the Banblade Cannon (which if you notice are complete rubbish in EA). It's not an especially powerful weapon not likely to hit but when it does contact, it gives everything 2 hits. The ability in 40k is called Blast.
In EW you, again, leverage a weapon level ability called Devestation Class (DC x) where the x is the number of damage it does when the to-hit roll is made. So this means you have another level of fidelity and options to apply, without resorting to an exception based rule like MW/TK that's simple to apply. This means you can have things that have a big boom but don't side step armour (or DO by applying both AntiArmour and DC) and don't rely on atrifically playing with the to hit roll to balance. It also allows you to alternate the likelyhood of performing TK/DC damage between target types as A/P to hit is still written out. The silly example in EA I like to use is the Volcano Cannon probably is perfect for representing shots at vehicles and terrible at infantry (which it probably shouldn't be able to do at all or if allowed, be very likely to not actually wipe a stand of infantry out). It sounds contrived until your titans face off against 'Nid gaunt swarms.
5. EA uses a special type for representing units that have more than a capacity to handle a single point of damage called War Engine (WE). That also comes with rules baggage as such units can't be mounted in transports, can be shot at regardless of more realistic targets in front (in the EA designer thought-process, WE are only HUGE things that tower over things like Titans). That's fine but what happens when you need something with more staying power but it shouldn't be able to take shotgun blasts to the grill? Good luck.
EW has the ability, regardless of type of unit to indicate how much damage it can take. Almost everything is 1 and is by default. This sounds contrived until you do something like model a super character from 40k (Dante or Calgar) or something like the Primarchs in the EA Horus Heresy supplement which had to jump through all sorts of hoops and contortions and special notes to deal with these super humans. In 40k this is represented by wounds and is independent of the toughness and the physical size of the unit. For no real extra work you've got that extra flexibility when needed.
6. EA has a set of special abilities that effect what a unit can do / behaves. EW uses a similar situation of these keywords and in most cases they are the same. EW however simply has more of them available and/or has taken an EA ability that has two effects, and broken them down into two independent abilities that we can apply. It's EA+++
This is important as there's plenty of units in EA that just are not worth taking in the game, don't work like their fluff and/or 40k counterparts work, and don't have any good way to fix them. The Baneblade is a typical example. It's a tank that is meant to always keep moving forward and doesn't generally bunker down and shoot and works in close cooperation with infantry on foot. It simply doesn't work well in EA and you don't seem them used in competitive situations. It took all of 20 seconds to fix it in EW as there's an ability called Totem that allows external formations working in close concert with that that unit to gain bonuses to rally. Basically Baneblades are the symbol that keeps the poor bloody guard troopers from breaking when nearby.
Let's take the EA Space Marine Captain. There's basically no reason for them when the option for a Chaplin exists. They're simply not worth 50points when +1 inspiring is available. However 25 points is too cheap. How to fix? in EA you just don't. In EW, there's another new ability called Tactical Genius that for each unit available on the battlefield, provides a boost to the rolls to see who wins the strategy for that turn. Boy, that sure does sound like what a Space Marine Captain provides in battle, huh?
Then finally there's concepts that do even have a analog in EA for interesting possibilities such as air controllers, secondary commanders, etc that again, open up new possibilities.
7. EA. Far more reliant on Configuration over Convention. EW uses Convention over Configuration. If it's not stated, it uses the default stats. This means in EW, 99% of the time you don't need any extra stats to indicate a unit capabilities and only when you're going to do something special do you need to indicate. It has the side effect of making those instances immediately stand out when you scan the stats. In EA there's a huge amount of special notes required while in EW, the number is less.
8. In EA, RA is just wrong. Instead of granting a reroll on failed save (unless hit by MW) in EW you get a reroll, but at a potentially different value. This is represented by using an Armour value of X+/Y+ where X is what you have to roll to save. Failing that, you get another roll for save but at Y. If you don't have two values listed then the assumption is that it the same for both rolls. See Convention #6^^ Basically it's yet another knob for balance and flavor that costs nothing to have available.
9. This is open for debate, but even among EAs fans (which I am one), it's generally admitted the weakest part of the game is the aerospace rules. They work but are known to be a bit rough. EW goes a radically different direction and uses aersopace elements as a strategic level resource that can be used a limited time in this battle and are fast acting and done. The way they're mechanically used on the table is by leveraging the tried and well regarded line strafing technique which does a great job of representing a craft that overfly the battlefield in a few seconds and is gone. CAP/Interceptions are able to be done the same but on an intercept course to the attackers approach. While not a perfect model it has the benefit of keeping the game FAST and focus on the ground elements.
10. EW has an additional rule that I actually think adds a huge tactical depth called Tank Shock. Basically it represents units with armour support in a CQB situation against enemies without armour. They gain a small advantage to their the suppression count going into the battle. Think of the scene in Band of Brothers where Easy and Charlie companies are dug in along a tree line. The SS panzer grenadiers perform a mech assault on the light airborne infantry of Charlie company that breaks due to the presence of armour elements. Well there you go
11. Slow Fire is wrong.
In EA that is simply a weapon that can shoot every other turn. Cool. What about weapons that can shoot every 3 (especially important for scenario play)? In EW that's simply a coefficient on the weapon (rate of fire) and not an ability. ".5x weapon C A(x+)/T(y+)" for a weapon that shoots every other turn (also can be written as 1/2). Every 3 would simply be .3 (or 1/3).
12. EW lacks some abilities
While EW is in most case a shuffled and rejiggered and rationalized EA, there's places where it doesn't have analogs. Specifically Expendable, Slow and Steady, and Mounted. I'm actually working to get them mainlined and in any circumstance, are able to be added in setting modules.
Pretty good set of rules too. [ I'm old ... I forget stuff ... 
]
