One of my favourite shows as well. It's completely different from almost anything I've seen before, and Michael C. Hall and the writers are brilliant in getting you to empathise and root for a serial killer protagonist. I can't wait for season 3, but I'm kind of hoping that's the last one as I don't want to see the stories start to peter out. I'm not even too sure where they can go following last season.
The show is a bit bipolar I find though. When it's good, it's really, really good (for example, most stuff involving Dexter and Doakes). However, Angel and Masuoka are two of the least interesting/most annoying supporting characters on television, and there are some ridiculous story threads from time to time like the LaGuerta/Pascale "there's perfume on my sweater! I CAN SMELL IT!!!!!" business from early season 2...
Thankfully, on the whole, the good outweighs the bad. The character studies of Dexter are riveting television, and if they would just cut out some of the lame subplots going on, it would easily be the best show on television, and possibly the best since Six Feet Under ended. Focus on the key character pairings: Dexter/Deb, Dexter/Rita, Dexter/Doakes, Dexter/Harry and (to a lesser extent) Dexter/LaGuerta; forget the rest.