I wouldn't say there's so little to do; more that there's more to see and think about than if you were just running through passages and levels pointing your gun, watching bodies fall. Have you bothered to follow the story, or are you taking short cuts around that? If so, you're missing out.
Of course, there are more action-filled games than this, but give it a bit more time and play in a different team to see if there's actually more to do than you thought. However, you are right, there are things Rare, the company, could do to enhance the action and I'm sure they will before long.