They say there are bugs, these have been fixed two days after release. Don't listen to GameSpot, read my review instead.
I bought this on day one, and even then I was impressed. The multiplayer elements didn't work at all - I have to admit, but I played on anyway. Two days later, however, and the game is completely bug free. I am playing Challenge and Adventure mode all the time with my friends, and we have found no more bugs or glitches, the game is now perfectly fine.
Sorry for the short review, but here is my Conclusion:
The game is now bug free, multiplayer is a blast (as long as you know the people you are playing with, and can trust them - beams across the screen are scary.), and the Adventure mode is quite funny at times. This is well worth the $10 I paid for it, and if you are looking for a fast paced action game, in the disguise as an RPG, you should look no further, Magicka is that game.