When I was a little kid, I always rooted for those kind, innocent folks as they ran and hid from the big bad monster. It was easy to put myself in their shoes and get caught up in the story. What if some hairy werewolf or giant lizard was after me? Why I'd run as fast as my pudgy little legs would've taken me. I wasn't so much identifying with the supposed heroes in those movies, I was really placing myself in their situation.
Now that I'm all grown up, I'm not so sure my method of watching a monster movie is any different. When it's an especially action-driven movie, I'm pretty much just looking to get sucked into the action and imagine myself in the same situation. For the slower-paced, more atmospheric films, then I'll pay more attention to the protagonists and try to go along with their storylines. There are movies, however, where it is extremely hard to root for the good guys. In those cases, I root for the monster.
A perfect example is Cloverfield. What, to me, could have been a spectacular monster movie became tiresome and insufferable thanks to vapid, unappealing characters the film followed from beginning to end--not to mention the irritating shaky cam style of filming. Accepting the notion that the "found footage" approach worked well, with a supposed camcorder used to document an alien invasion in New York City, there is still the problem of giving the audience characters that they can root for. I really had a hard time liking any of those people in the movie, and I quite frankly relished in each of their deaths as the story progressed.
In a movie like The Mist, where hordes of insectoid and cephalopodan creatures prey on humans, there are a few core characters to rally behind. Thomas Jane gives a particularly good performance as a father who must hold his own panic at bay for the sake of his son, but for the sake of a slowly degraded social structure inside the store. It's those other characters, the malevolent and apathetic ones as played by Marcia Gay Harden, that make it all the more easy to root for those macabre critters to pick them off one by one.
I suppose my willingness to join the monster pep rally dates back to my empathy for Boris Karloff as Frankenstein. The big lummox wasn't so bad--once you got to know him. Is it so hard to imagine a sympathetic side to some of those other monsters in movie history? I mean, King Kong was a victim of celebrity, wasn't he? And how about The Thing? Wasn't that alien only a victim of circumstance, trapped in the arctic after crash landing? Okay, it was a real dick when it thawed out, I'll grant you that, but all that proves is that the Thing is not a morning person--I can relate.
More often than not monsters will want to eat you, but let's be honest ... you kind of have it coming.