I completely agree
Some of the bits where they were escaping from the orcs underground (the ladder, sweeping the big pole from side to side, etc) felt like they were just in there to look cool, and it didn't have the same "part of the action" feel that the escape down the stairs in Moria had in FotR.
. The bridge/ladder stuff felt like a Mario video game, while the action scene with collapsing staircase in Moria was fantastic, one of the best scenes to experience in a theater.
What's more, it works subtly to develop character as well as being an action scene.
- It gives Legolas a true "Robin Hood" moment, complete with the camera following an arrow (in the dark) to it's target, so we know without a doubt how good he is!
-It gives a bit of the rivalry between Legolas and Gimli (that Legolas has to pull the beard to save him) that will pay of in subsequent films... not to mention the "No one tosses a dwarf" bit which, apart from being funny on it's own, also pays off in the next film.
-My favorite bit of character here is the fact that Boromir grabs the hobbits Merry and Pippen and bravely jumps the gap. He had been building chemistry with these two along the journey to this point, training them at the campfire, but this moment really is a fantastic little hint of the sacrifice he will make to save them at the end of the film... a sacrifice which will pay off all the way in the third film when Pippen offers to serve Denethor in payment of Boromir's sacrifice.
-Plus, Frodo and Aragorn are the last to cross, and they are alone for a moment, in a way, just as they would be for a moment when the Fellowship breaks. They both have tremendous, albeit, separate responsibilities which will weigh on them heavily throughout the other films and they are both very much always separated metaphorically from their friends.
Now, of course the "Moria collapsing stairs" bit wasn't in the book,, but, as I've demonstrated, it's a fine example of screenwriting, of making something for the screen that's exciting at the moment but also serves character.
The underground bridges scene in the Hobbit
was not nearly as impressive.