I have actually played a serpent spam list for the last 10 games or so, refining it. I have tabled the enemy in all games barring a 4-3 loss to necrons, the bane of the list (needed an extra turn to table him). The main problem it faces is killing flyers (the whole dex has that problem) and defending vs assaults.
My list at 1850 is
Autarch: bike, mantle, lance, mask
6 x 5 dire avengers
6 wave serpents with holofields, scatter lasers and 3 of them with shuriken cannons
2 wraithknights

First of all: the autarch is not a very good option. The farseer is superior, but due to points I can't seem to cram it in here.
To everybody that dismisses the DA, they aren't playing them to their full extent. What you do is identify the correct pieces of terrain and disembark them turn 2. You certainly do not want to be standing in the serpent when it dies, since it will most likely be stunned in the process, rendering them useless in the following turn. Once you find a wall anywhere, it really is easy to keep them alive using battlefocus and small unit size + 18" range. They really put a dent in the enemy army turn after turn and I have yet to lose more than halve of my scoring. When you have the enemy's broadsides shoot SMS at 5 DA over shooting their missile spam at a wave serpent, you have forced a bad decision.
The wave serpents are pretty self explanatory: they kill shit dead. That they do very well. Tau armies fear them for a reason.
The wraithknights are probably the best miniature in the army, though. Their killing ability during one given turn is normally unimpressive, but during the course of a game, you tally their kills and they really are amazing. They are the heavy tank killers, normally in cc. Wave serpents can't take on land raiders and fire dragons are inefficient since you have to suicide them and their transport to kill a tank. The wraithknights will die to whatever is inside the LR, but it is dead turn 2 for sure, unless you get lucky and punk it with shooting. They also are essential to stop the popular screamer council from tabling you without even having to think about it. You put a wraithknight into the screamers and forget about them. They will eventually kill it, but he won't have anything else left by that point. Plus, if some inexperienced player uses khorne dogs without a khorne herald with the khorne axe in them, happy days!
I once managed to kill fateweaver and a tzeench daemon prince turn 1 with them. The wave serpents dropped another prince and a good part of the screamer unit. The alpha-strike potential of this list is very high.
Now, for the bad: this list will lose to flyer spam, mainly the helldrake - nightscythe kind. It cannot kill flyers fast enough, and s7 that can reach you is bad news, unlike broadsides, who have s7 in spades, but die easily the second they move to put themselves in range.
Rending resilient assault armies might give you a problem if they go first. 18 wraiths are a problem if they go first. However, if the serpents and wraithknights get the first shot, they will not reach you. The good thing however is that necron wraith armies seem to be going away fast, since tau beat them something silly.

Nowhere does it say melee I think, so death magic will de-mage enemy mages. Sure, they may as well be dead, but a Slaan life or a greyseer on a bell is not going to bother dispelling the 2d6 4+ to wound. Then they realise they are no longer mages.

I'm from Spain and the stop of Maelstrom doesn't affect me (although clearly I don't see the reason they are doing it...don't they earn the same from internet purchases?) I, however, get 30% off from Maelstrom. The price hike obviously affects everybody.
What is really fun is that today I found an interesting chinese website you may want to check out: http://www.miniatureshobby.com/index.php?main_pag...
Now I'll wait and see if somebody purchases from them and I can see some review.

Land Raider might be a problem with no melta. You have a lot of rending but those 6's sometimes don't come up. I have had some success with 3 meltas in chimera with flamer. The same thing I use in my IG, just a lot cheaper and with GK's around to say don't come close.