To say the acting was bad is a little silly, considering it's usually not great in Smith movies. I mean, the acting in the first Clerks was pretty bad (I still cringe at Dante's girlfriend saying 'See you when you get off then' twice in like 10 seconds at the end).
Probably the best acting in a Smith flick is Affleck in Chasing Amy, and that's Ben freakin' Affleck, not exactly known as the next Sidney Poitier.
I agree O'Halloran isn't a great actor, but he wasn't in the first one and he wasn't in Mallrats, so why would you expect any different?
Anderson I think nails Randal. Keep in mind, he is just a guy that Smith knew and he agreed to be in the first one because Smith thought he was funny. I know he does movie stuff now (directing and such), but he's not an actor and never has been. You can't expect too much from him.
I agree that Mrs. Smith shouldn't have had that big a role, though I thought she was servicable.
I also though it was their daughter looking at Dante throught the window.
Overall, I thought it was a good movie and well worth both your time and money. I'll be buying the deluxe DVD.