I had a similar experience playing Psychonauts; it was still a great game, with a few memorable moments/lines, but I'd knock a point off for the end section. The game itself required coordination and sometimes timing (easier using a gamepad than a keyboard/mouse), with only a couple instances where I had to go through a part multiple times to get it. The only pre-final level section I got frustrated enough to swear at the game became a fair bit easier after I mapped a 're-centre camera' function to one of the gamepad buttons (had to walk/jump along a rotating structure).
For the final escort mission I tried it a few times, but between the twitch based timing required and NPC AI (that often had him run directly into the opponent before you could get anywhere near him), I was soon looking for cheats to boost the countdown timer and/or friendly NPC health. Failing to find either, just lots of similar problems, I ended up watching the end section of the game on YouTube. Initially checking the video was just to see what I should be doing, but there was no frikkin way I was going to duplicate the timed twitches necessary to finish the game, so I quit.
I'd still probably get Psychonauts 2, in the unlikely event it ever gets made.
