It's fun. Really. It just is.
Wakfu is... well, it's difficult to describe exactly why it's so good. I suppose you could think of it as a spiritual cousin to Avatar:TLA. It's an Animesque French production, with a solid cast of characters, following a (so far) season-long story arc. It's got some of the most fluid, cinematic-quality animation (in Flash, to boot!) this troper has ever seen, a ridiculously catchy soundtrack, and, though it isn't by any means cerebral, gawd is it ever fun.
There's a certain energy to the story; it's got your classic Five Man Band, with a shonen-type hero, but it's all done so energetically and with such good humour that it doesn't feel cliche. The heroes are a diverse bunch, and, though the show is intended for a fairly young audience, there's juuuust enough shipping and getting crap past the radar that ot's still fun. Oh, and it has one of the coolest villain's this troper has ever seen in a fictional work, ever.
Anyhoo, to sum up; silly, not too serious (except in the later episodes), but energetic, fast-paced, and, above all, FUN.