So as the title suggests, Im going to look at the Eldar units FW is producing as alternatives/supplments to existing GW models. FW models I will not discuss are the space fighters and the titans, as both are not part of the GW line and belong in Apoc games.
1) The Vyper
The Vyper is the black sheep of the Eldar, I dont think anyone could argue otherwise. Its open topped and has such low armour, a bolter could stop it. What's its role? Fast attack that can utilise heavy weapons. However, its rules for heavy weapons is still too high and quite frankly, even if it does occupy the least used part of the Force Organisation Chart, you're better off taking War Walkers with 2 Scatter Lasers.
The Hornet is not open topped and has higher armour. It has the choice of the pulsar laser (although personally, I wouldnt put something as expensive as that on the Hornet). Heavy weapon costs are the same but I dont think anyone expected that to be changed. It starts with Star Engines, which is a big point and only costs 10 points more than the Vyper.
2) War Walker
The WW is actually a solid choice. However, its BS is standard of Eldar (which I think ought to be higher, the Eldar are not Guard after all, and you would think those extra years of life and training would have done something for their marksmanship). Weapon costs are usual and hardly surprising. Its weakness is that it occupies a HS slot which on higher point games, I really would like for a Nightspinner in conjunction with 2 bare Fire Prisms.
Solution: Wasp Assault Walker
Discarding Scout USR for Deepstrike, and in addition having Jump Jets, the Wasp is much more mobile. Armour remains the same, but the BS is bumped up to 4, which makes it much more lethal. Base cost is the same as the Vyper as well! Armour, weapon costs are the same, but thats absolutely fine. Using Wasps with Shuricans is very viable (I have had 4 games with Wasps now. I have 4 Wasps, I ran them in 2 squadrons all with Shuricans just to try them out. Another game I used Starcannons to great effect.) Furthermore their jump jets can be used to escape, or basically charge units that have no melee weapons worthy of damaging the Wasp. The biggest point is that they are NOT HS, they occupy troop slots. As it stands, FW have added the most reliable way to add dakka to any Eldar army.
Edit: Theyre awesome with EMLs as well.
3) Fire Prism
There is nothing wrong with the Fire Prism, the sticking point is what Eldar do with that 3rd HS. 3 Fire Prisms is overkill, although nice. Most will opt for WWs or a Nightspinner, which is a brilliant weapon in its own right. However, FW decided the Eldar needed something with even more killing power.
Solution: Warp Hunter
It has a D-Cannon. What else can be said about it! Adding a different template weapon for your army is very nice, the D-Cannons are the most destructive dakka the Eldar have to date. It's a short range main battle tank with superior mobility compared to equivalents and fufills a different role to the Fire Prism which is long range.
4) Long Range Anti-Tank
The Brightlance is lacklustre for its points costs, using cost-benefit analysis its not worth taking. So what do the Eldar have against AV13-14? Fusion guns and practically nothing else, EMLs if youre damned lucky.
Examining long range infantry that take HS... Well we have the Dark Reapers - which are nice but pricey. They are MEQ killers not AV14 killers.
Solution: Shadow Spectres
These are very nice, but the big thing for me is that they have an awesome Phoenix Lord, recently released called Irrilyth. See the existing thread on him.
Anyways, their Ghostlight has insane range and AP1. If that hits, that tank is going to suffer. Although their rifles by themselves are not very long ranged.
The exarch can take an improved prism rifle (ie, the prism lance) or a haywire launcher. The launcher I cannot make much head or tail of it. It appears to be a disabling weapon to be used in support of other units, such as Fire Dragons.
As it stands, Eldar psykers can give wraith sight to our most devastating and threatening units, the Ghost Warriors. Psykers are Farseers or Warlocks, but requires those flesh pods to babysit wraithbone war constructs. Sure, you can add a spiritseer to Wraithguard, but what about Wraithlords? It is not a problem per se, but an inconvenience or weakness at most.
Basically the spiritstone of a Warlock in a wraithbone construct, the Wraithseer is a HQ unit and is devastating. Althought it requires another HQ choice to go with it, it is in its own right more powerful than the Avatar. His psychic powers are truly awe inspiring too.
6) GEQ units
We currently have the Defenders, which are a reasonable choice, but have short ranged Shuriken Catapults, and Stormies which most will take because of their cheap Special Weapons (especially the Flamers).
The rules for these have not come out yet, but judging from what arrives in the conversion kits and the photos on the FW website, Corsairs will have access to jump packs, flamers, fusion guns, and las blasters. The lasblasters appear to be a remedy to the shuriken catapult's dire range. Many would argue that Guardians would be better off with Lasblasters - well here is your solution. People who use Stormies just for their guns will be glad to see the Corsair models have Special Weapon choices. Discarding the redundant melee and keeping ranged weapons, you have a mobile shooty squad. Corsairs can also take a EML or Shurican (hypothesising).
Until we get a new codex, FW is filling the niches which will all culminate in IA11. Experimental rules and the new models can be found on the Forgeworld website. Check them out