The Swordwind Biel Tan were considered to be somewhat overpowered; went through extensive discussions and were modified in the official 2008 changes that are reflected in the GW site (free download). The main changes were to drop Spirit Stones altogether and amend 'Pulsar' to be 2x shots on the relevant weapons (there are a number of other minor changes to particular units).
Eldar were always intended to be brittle but very powerfull if allowed to maintain their strategic aims; so called 'soap bubbles' armed with sledgehammers. As such there are three cardinal rules:-
- Keep the BMs on the formations to a minimum by extensive use of cover and Marshalling
- make best use of the various special rules especially 'Hit-&-run to achieve the Eldar speed advantage
- Only assault when you are certain of winning; which also means keeping safe and preserving the army until that point.
Eldar work best with a high activation count, ideally achieving a 2+ advantage over the opposition. However the various army lists all force hard choices on the player, so at 3000 points or less you are usually only able to play to a single strategy and choose formations accordingly. On the whole, the Eldar tend to work better in higher point games; at 4000 points and higher, players can choose armies with multiple strategies which makes the list both more flexible and more powerfull.
While the rules force you to take warhosts, always take at least one set of guardians to be able to use the Farseer rules (second retain; the Avatar; 'commander' and strong unit capabilities).
- 'Naked' the guardians are very vulnerable, but can be a usefull Blitz guard especially if the Blitz is a Wraithgate and three such formations are kept off-table.
- Upgraded with Wave Serpents they become a very potent strike force; with the guardians inside the WS for protection they have a 55cm assault range (35cm move, +5cm disembark, +15cm FF), though recommended practice is to dismount behind the WS to ensure that the first 4x hits are absorbed by the WS armour
- Upgraded with WraithGuard and or Wraith Lords, they are a very potent assault force when deployed from 'Gates (Wraith Gate or Storm Serpent), though these can be countered, which is why you should always take several 'gates if using any.
- Put in Vampire they do make a good strike force, but the Vampire is very vulnerable to AA and the (hopefully) victorious Guardians equally vulnerable to enemy counters. As a consequence this is probably the weakest strategy. (Though I agree with Steve that Aspects in Vampires are deadly).
Aspects and how to use them is are a complete thread of it's own. You should also always have at least one Aspect warhost to gain the Autarch and the Supreme commander reroll. After that they all have strengths and weaknesses, though the Warp Spiders are arguably the best and the Banshees arguably the worst (though still very strong if deployed in Wave Serpents).
Regarding the other formations; I always take at least one formation of Rangers, and usually a Void Spinner and one set of Night wings (though this latter depends on whether Spaceships or Titans are to be used).
Fire Storms (with Falcons) provide good though brittle AA that needs to keep in cover as much as possible; Fire Prisms are even more brittle (though longer ranged), but a very good deterrent to Marine THawks and Ork Landas.
Jet Bikes are an excellent support formation:- double and shoot (with a Vyper) to place a BM, repeat with a second formation, then assault with warhost of choice; a *really* deadly tactic is for Guardians in WS to use Commander to order a combined assault with two Bike formations; when victorious the entire lot can consolidate to support a further assault. Combine this tactic with Shining spears and further bikes and you can take out titans through shear assault firepower.
(At one Britcon in a 4000 pts army I took this approach to an extreme with 8x bikes, 3x Guardians in WS, Shining Spears, 3x Rangers, Void Spinner and Night Wings. The main problem being moving all the formations and processing the large attacks it generates).
The Eldar are probably my favourite army because of the variety of strategy and tactics they can use (see Steve’s lists as an example). They are also my least favourite because of their 2+ initiative and my almost legendary ability to roll ‘1’s
