I have left many a game just to check the objectives of a level. It would be handy to have a button somewhere to press to bring them back up. If it already exists, maybe it should be easier to find.
P.S.
******POSSIBLE SPOILERS******
The level Ship Crash is rather unclear on the objectives. I made it to the end without using the lift, or attacking the ship's panel, but I did destroy the 2 purple generators(they may not be required?). It wouldn't let me finish the level until I went back and destroyed the ship's panel (under the sand, between some clonium). Very unclear level, and the on-screen in-level text isn't very clear either. Thankfully this level is not on the main path to the boss. Perhaps this level needs better objectives, seeing as how you can leave without doing certain things but then the level will never end (I also tried hitting the invisible switch on the lift (as in, the lift was still in the top right, and I did not attack the lift panel). I also destroyed the stuff that is under where the lift moves too, and that did not let me clear the level.
I tried destroying the ships panel my first play through, but I did not see anything to alert me to an incoming change in the level, so I went back to my checkpoint =(. Big waste of time.