The design is decidedly NOT for hardcore MMO gamers, but it is a great pick-up-and-play MMO, which is pretty rare.
Any serious MMO player, who likes a powerful guilds, elite loot, PvP ladders, smack-talk, RvR. You'll get none of that here.
Wizard 101 is designed from the ground-up to be very kid/family safe. All communication is filtered. Non-subscribed players can only communicate using a menu of template emotes and expressions, like 'Hi', 'Bye', 'Yay', and so on. Subscribed players are able to chat with the keyboard, but even that is so filtered it's impossible to say anything even remotely offensive. Numbers and bad spelling of words is even prohibited.
There is no crafting, no guilds, no in-game email, no item trading or auction house.
So that's the bad.
The good is the beautiful, richly colored worlds you get to travel through. A really fun and addictive turn-based card-battle system, which is like nothing else I've seen in an MMO before. And open grouping in battles, which means anyone passing by a fight can jump right in and help out, which I think is a great idea.
So that's what is boils down to. A unique, simplified, very friendly/casual, battle card MMO. One of the few online games where restrictions on your time shouldn't impact the fun you can have.
I really love this game so far. But again, if you Play-2-Crush, this isn't for you.