I think the thing that keeps me watching is the "how the hell are they going to get themselves out of this latest trainwreck they've gotten themselves into?" Also, the characters are always on the edge of beating the living shit out of each other (and sometimes they do), and that's entertaining too. I'm twisted that way. ;)

I loved SG-1 and Atlantis though. Some of the above applied as well, but there were also a lot of characters that I just adored. Most of them, actually.