keviny01: The most notable additional location is the "fireball room" at the Mayan site, which you don't see in entertainment mode. You have to dodge fireballs while avoiding lava pools below. Some find this challenge annoying enough to want to avoid playing in the game player mode altogether.
Huh, I played this years ago, always in gamer mode since I love challenge/puzzles, didn't realise this was skipped entirely - might have ALMOST been worth it. Still doubt I could have brought myself to do play in entertainment mode and miss out on the other goodies though...
keviny01: In the Roswell base, you get into 3 labs in entertainment mode, but 4 labs in game player mode.
At Autotec, you need to go into a closet to get soap and water to make the floor slippery so the guard will fall down and pass out. You skip all that in entertainment mode.
I could be wrong, but I think there's another location that is only available in gamer mode. Unless that "shack in the forest" with that "film clip" (want to avoid spoilers here) is also available in entertainment mode...
That location features a small number of extra puzzles plus a "movie" of sorts. It's pretty-much a self-contained location and is only there for plot background, but it's pretty cool IMO.