I agree with HFR that the UI should have an appeal to older players. Right now it looks like your trying the same approch all the Pokemon merchandise that was aimed at 5 year olds took - using bright, solid colors, and all the obnoxious unevolved Pokemon. Really, don't use pikachu in the UI, and if you use any Pokemon use the ones the still seem relativly cool to all the ~15 (or even 21 >.<) year olds that use this site will still plan on using, such as Charizard, Blastoise, Venusaur, etc. And if your planning on using Pokemon in the UI I would suggest using the watercolor versions or in-game sprites.
Although I'm not sure if you should even put pokemon in the UI. If your looking for other ides for the borders of the UI the Pokemon cards actually have a lot of background/boarder space as well, and barrowing ideas from the Pokemon/Trainer/Energy cards could probably look pretty cool as well. The cards are also a good source of cnp material for creating quick icons as well, so they are worth looking into at least.
The cloudy effect in the backgrounds of several cards would add a more impressive textured look the the UI, and I think that would offer a more soffisticated/WC3 feel.