Haven't quite got through season 2 yet, but have to say that the second series is a big improvement on the first one. It consistently started to hit high notes right through the sophmore effort. I also thought the first episode of series one was excellent - one of the best debut episodes on a series for quite a while - but thereafter the writing in series one was patchy.
Think they got the guy from 'Malcolm' because of his comedic ability, but I'm very happy the series went darker in the second season. The acting from all concerned has been damned good - loved Tuco's uncle in the wheelchair with that bell! The bloke from Malcolm is a very, very good actor and I bet he's glad he's been able to showcase his dramatic ability in Breaking Bad.
Don't think anyone has mentioned the soundtrack yet - it has some cracking tunes on it - it's worth watching just for the soundtrack alone, let alone anything else this series has to offer.
Like the other posters on this thread that have recommended this, Breaking Bad gets my seal of approval as well, so long as you can get through the up and down quality of the first season to get to the excellence of the second.