So far the single player mode has been "meh" for me (less double battles, please. Oh, and adding another vote against the Neon Colo).
Random Wi-Fi battles have actually been pretty fun, though. Aside from 2-3 of the 15 or so games I played, there wasn't much latency. Only one person disconnected on me before the final blow (and a different person used the "Give Up" option, which I prefer since I don't have to sit through the timer).
My favorite battle so far has been My Magnezone killing a Giratina and then my Vaporeon single-handedly toxic-stalling to death a Palkia and Lugia (after poor Mag fell to an Earth Power mispredict and Breloom to an ice beam). The battle itself sucked because it was one of those 2-3 that were laggy as heck, and stalling is boring, but it was nice to see the little blue guy pulling a win against an all-uber team. I'm glad I picked toxic over ice beam! I'm also glad/impressed that the opposing player didn't disconnect and actually stuck with the laggy boring stallwar til the end.
I was expecting the worst, with every team on random wi-fi being all ubers, but I've only encountered one all-uber team, one team with all top-of-the-line-OU, mostly teams with a variety of OU with some BL pokemon, and maybe 3 teams using the rental cards. Overall it's been pretty fun.
It makes me sad that I have to go back and do more single player to get more "money" and to unlock more dress options. I'm up to the Sunset/Magma Colos right now... thankfully only a few more to go til I should have everything unlocked, and then it's a matter of finding the best way to get the points to buy everything.