I don't remember exactly. Maybe the levels do carry over. But you can max out in the first game, in a given area, fairly quickly and it doesn't do you any good. Not max out overall, but max out for the area.. in the later areas (first half of part 1 is easy). The Bat boss in the mines is a bastard because of this. I recently played through the first part and mostly into the second part, so maybe the numbers look the same but the leveling system is not as balanced as the second part. The leveling, related to the area, related to the boss for the areas, was more even in the second game IMO. Though the second part has its own different set of challenges.
Then again.. maybe I'm just imagining all of this ;>_>