So yesterday I took the exact same list I used against Dennis last Friday and put it to work against Jason's Tau. I'm going to be completely honest: I expected to really pound him out, and I did. There were surprises along the way and it was a closer game than I thought it would be, but the end result was the same.
As I did the last time, I rocketed four Wave Serpents into Jason's deployment zone, bit down on a belt to withstand a turn of shooting, and then let the clown party loose. Constant point: If you have two large Seer Councils running wild in your deployment zone, you're going to lose a lot of stuff fast. Broadside team and Crisis Suits were gone completely by the end of turn 2 (when my War Walkers came in, by the way).
Jason's vehicles presented me with a challenge that was a little tougher than what Dennis offered me. What I didn't expect was the Flechette Dischargers, which cause hits on the assaulting unit before my hits are resolved. My first three casualties (all Warlocks) were from this. Jason's also been running a Kroot-less list with O'Shovah and he strikes with considerable precision, so I lost a transport, a squad of Storm Guardians and almost all of one Seer Council. Personally, I thought O'Shovah wasn't as interesting or effective as Kroot would have been. I fear those far more.
The game ended on turn 5 (so it was a short game because we both deployed nothing on turn 1, so our turn 2 was really our turn 2), and in the end I'd blown up some vehicles, killed his scoring units and picked off several other units along the way.
Eldar players, take heed: This is the first time I wished I'd used at least a couple of Singing Spears. On at least two occasions I was close enough to a Devilfish or Hammerhead to pop it from close up, but just couldn't catch up to it in close combat. That's the only change I would have made, list-wise, but I also played through a few dumb mistakes: I have to start thinking about what I'm supposed to do after after the transports dump out and all hell breaks loose. As it was, I didn't do a lot of thinking ahead in this game and found myself dispersed and a little unfocused as the game drew to a close. Jason's a smart player, so he knew when to turn his vehicles to keep the front arc facing enemies, throw intervening models between assaulters and their targets, and how to use cover against me. If I had played smarter, I would have kept the pressure on until the end instead of coasting on the successes from early in the game.
In retrospect, there's no arguing that this is the most powerful list I've used in 4th or 5th ed. Whatever it is you have in your deployment zone as you start the game, this list has the means to a) Get to it quickly, b) Destroy it easily. The only thing that can stop me from delivering my biggest fist to the enemy's face in turn 2 is if the dice rolls are bizarrely against me. To really refine this list, I need to start playing against armies with more unusual first-turn deployment, such as masses of Imperial Guard or Drop-Podding Marines. I think that either spreading targets out or massing so many targets that I can scarcely hit them all will be my foil.
Naturally, there are always going to be those macho men who boast "That list isn't bad. All I have do is x, y, z and I'll crush it", but I think that so long as the dice remain statistically average and I don't switch off my brain after turn 2, these Eldar will be hard to subdue.