I had a lot of fun playing Nightmare Troubadour (a DS Yugioh game). It was early enough to not be completely nerfed by the advanced format, so there were lots of really fun decks you could build. My favorite was a one-turn-kill deck that involved sending a bunch of cards from your deck to the graveyard and then playing Reversal of Graves. Usually it failed miserably, but once in a while it won spectacularly.
It almost makes me want to go see what's out there in terms of online TCGs.