I disagree that the later levels are filler. Episode 4 is my favorite, because it's the episode that best shows off Quake's excellent movement. It's less crampe

I disagree that the later levels are filler. Episode 4 is my favorite, because it's the episode that best shows off Quake's excellent movement. It's less cramped than the others, and has better "flow", letting you bunny hop all over the maps with minimal waiting. I agree with the common consensus that it's the ugliest of the episodes, but I think this suits the weird otherworldly theme that Sandy Petersen was going for (influenced by the works of H. P. Lovecraft). The only real complaint I have is the use of the Spawn enemy, which is generally considered the worst designed enemy in the game. But the enemy placement in episode 4 has the advantage that it makes relatively little use of the Ogre, which I consider the second worst enemy, because it has too much HP for something so common, and is too predictable on Nightmare difficulty (to the point that some people say Hard difficulty is actually more difficult than Nightmare).