I have no problem watching underground again
underground?
If you mean underworld, its probably because its more a portfolio of gunfights, rather than a comic book. Hellboy tries to be a tad more like a comic and builds the character up, a bit like Hulk. hulks a bit more unapproachable for the same reason.
Spiderman and Xmen aren't so much like a comic book either, and the sequels are just the same movie with some sparkly bits cellotaped on (ie more fights).
Then again sin city doesn't have that problem really so it might be because they're not very good they aren't very easy to watch again.
The other but more likely explaination is that they had all the flashy bits and initial appeal, but then on repeat viewings (or lack of) you realise how shallow and stupid the movies are, and its not really got any appeal anymore. That's pretty much describes most hollywood movies.
Sin City pounds the others into the ground though, hulk smash indeed