First of all, I'd like a game with:
-2D gameplay (Graphics might be 3D, there's IMO no problem with that),
-Oddworld atmosphere, you know, dark, dirty corporational buildings, sligs warehouses, mysterious spiritual forests, fate etc etc.
-Level and atmosphere of common brutality not lower than in AO/AE
-Great, smooth character/enviroment animations
-Hard to find secret arenas, mudokons/somebody-else rescuing
-Puzzles and game difficulty equal (or higher!) than AO
-No quicksaves, only (good placed) checkpoints
-Good/Bad endings dependable on player's choices
-FMVs with the sense of humor
-Awesome, memorable music
-Nice story and story-telling
-not simplified (like in MO) Gamespeak and A.L.I.V.E-like interactions
-final touch, polished product
That define an good Oddworld game for me, (I think... did I miss something important?) is it really that much?
I think underwater levels are a good idea as long as they're made wisely...