I bought the game about 3 weeks ago and haven't run across one glitch at all yet. The main issue I have is properly connecting to games when doing an online run. Especially invites from people on my friend list.
I have had a few times it froze, but not when playing single player, it would only happen when I was playing someone elses game.
If you do plan on getting the bloodbath DLC I would suggest doing it before playing the game through. Its a great way to earn money which can be a major pain in the ass and gain some good experience as well. I don't see much use for it when your game is done and characters are leveled to where you want them, seeing as it adds no real value to the game itself... unless you just want to kill wave after wave of zombies all day or just get the trophies like I did, then have at 'er :P (A platinum without a 100% completion due to dlc drives me nuts *cough, uncharted 2, cough*
It's time for another good idea/bad idea.
Good Idea: Eating a bear. Bad Idea: Trying to eat a bear while it's still alive.