a good point was made here. concepts and coherent style.
thats what i miss with most indie games. you need to have a cocnept, an idea how your game should look.

also, another good point wwas level design. i can clearly tell through the level design of some games if a pro was at hand or a trainee. a good level designer creates a level that consists of unique rooms. none of them look the same, and backtracking is reduced to the minimum the game requires. i find it often annoying in indie games that you have to run through the level a gazillion times to lengthen the game. this just sucks. reduce backtracking. its bad level layout and bad gameplay, and gameplay is frankly, all we have...