Mothim is just too good. That has to be toned down when it's released in english.
In other news, Rain Dance is (almost) back in the form of Water Drip! I'm expecting good combos with that.
Why did they have to make Jumpluff's attack 2 Grass? What made it brilliant was the 1 energy attacks, but now, I cannot discribe how disgusted I am.
I quite like the new Ludicolo. A small combo to do more damage is any stadium, followed by a Memory Berry/Harass attack, then 80 next turn. Not the best every combo, but it's alright.
Quick question, will it be possible to use 4 East Sea Shellos/Gastrodon and 4 West Sea versions? If you can, then that combo is brilliant, otherwise, not that great.
The Nidoking is quite good. Add Nidoqueen (DP2) and (DF) for a powerful combo.
If Grass decks become popular, Muk is the latest tech against them. Posion them, then stop them from retreating. Could work if you're lucky.
Unown N is strange. Nod could be useful if you have one prize cards left, but then your opponent won't agree to the effect, making it uselss. Unown Z is a tech for every deck to stop decking out. Then you knock out your opponents Entei(DP3) or they play Rhypherior to stop it's effect. Great stuff.
No Gardevoir is a bit of a surprise considering the Ralts line plus Gallade is in the set. Another surprise is the fact that Golem is in the set. Strage.
Trouble against Tool decks? Worry no more with Tool-worthy-Pokémon-away (otherwise known as Donphan). Only to be used in extremly metagaming.
Flygon is nice. Now if only Weezing (DX) stayed legal...
Darkrai LV.X is obviously insanely powerful. For best results, use it with Weavile (DP1). It's just too good.
Those are my highlights of the set (apart from the Jumpluff). Others have probably hidden themselves from me, or I just don't think will actually be any good.