I played through the whole trilogy recently and I can confirm, while the light/dark worlds gimmick of MP2 is quite cool, it's a pain in the ass, mostly in the early game. Good luck finding those keys, I recall I had to use a guide for one or two of them because of how weirdly it was hidden.
If you can play Prime 3 be sure to do so, it neatly rounds up the story across the previous games and has some good gameplay changes that make it more enjoyable (not having a gazillion weapons and visors for one example).