Here's what I've done so far.
1.) Get stuck repeatedly right at the start of the game, because the first NPC you meet was glitched
2.) Have bits and pieces of quests go missing, making them unsolvable.
3.) Invincible boss npcs with infinite hit points
4.) Invisible exp walls, I've hit 10 and it simply doesn't go farther after that, it just stops
5.) Random quests break in multiplayer, desynching me me from those I'm playing with and making me have to drop to single player to try to catch up.
6.) Had all my skill points vanish.
7.) Totally forgot this one, if you customize your win7 at all, your game...WILL NOT SAVE YOUR DATA. GENIUS!
I'm now on my 8th character, six of the ones before that are glitched and broken, unable to progress in the game any further, so I had to stop using them.
Other than THOSE things, it's an awesome game I guess -_-