Psychonauts is a terribly flawed game that also happens to be in some ways brilliant and one of the best platforming games I've ever played. The main issues with the game are issues that plague a lot of games from this era- camera controls sending you off a cliff, wonky platforming sections, etc. But the core concept is so smart and well executed that it doesn't even matter.
This game was in many ways way ahead of its time because it takes place in a retrofuturistic 80s setting and has a strong emphasis on narrative among the different characters. Back when this came out NPCs were a lot more robotic. It's cool that in this game they move around and what they say changes as the game progresses. The story is also pretty fantastic because there are more developments as it progresses. Normally in a game like this the setup is everything, for example, Mario needs to save the princess. However, psychonauts story is more akin to one you would find in a point and click game as there are consistent developments that change the characters.
The game goes pretty deep into Jungian psychology. All the character levels are stored in a main hub called the "collective unconscious" and each character has some unresolved issue in their psyche that makes up the bulk of the level. For example, one character is completely focused on being mentally neat and orderly but goes nuts when that order is upset by the protagonist Rasputin. The humor in this game is actually pretty well done, I laughed a few times at the overall silliness of the story, and if you pay attention there are a lot of visual gags that are just brilliantly done. For example, the senior agent is hiding around the camp in different disguises. When you confront him in the underground area, he claims he cannot go above ground and is trapped because the psychic crystals underground are keeping him sane. During the end sequence, there is no explanation as to how he's above ground, but you see a crystal strapped to his back as though he found a rudimentary way to solve the problem, but occasionally just says insane things. It can be inferred that he is actually crazy and goes up and takes on other roles at the camp without realizing it. There are tons of things like this in the story and it's really a ton of fun to play a game that rewards you for paying attention.
Likewise, the platforming and combat aspect is just great in concept, and only somewhat flawed in execution. Attacking can be a little unresponsive, but this game is more platforming than combat. As you progress you get tons of powerups like the ability to levitate on a bouncing ball and pick up and throw objects with your mind. Beyond this just moving around in this game is more fun than it ought to be, as Razputin can swing, slide down rails, double jump, climb, hang from ledges, etc. It's probably the most impressive number of individual acrobatic maneuvers I've ever seen in a 3D platformer. Further, as you progress you get more upgrades and become more powerful. The game gives a rank from 1-101 which is like a level that bestows new rewards as you progress. It's really well done and makes collecting everything in the game a lot more fun. This game has thousands of collectibles and for some reason collecting things never gets old in this game. I like the idea of collecting "figments", which are basically little two dimensional drawings on the 3D plane that represent ideas. Because each figment is unique it makes the collectathon aspect a lot more fun. I used the guide on Steam and found all the collectibles with few issues, but it was very time consuming.
This game also has some great boss fights, and I like that there are sequence breaks to certain problems, ala, Mario 64. Once you get the levitation ball you can skip a lot of the platforming requirements you'd normally have by jumping and floating over them. For some reason this is more fun to me because you can come up with your own ways to solve the problem. And while the overall structure of the game and its upgrades feels ridiculously confusing at first, after a few hours I found it highly intuitive and cleared the game 100% without any issues. It's clear that this game has a cult following both for its fantastic game design and characters. There is enough content in here for five platformers and each "brain" you go into almost feels like its own little game. I would put it up there with games like Banjo Kazooie and the original Spyro trilogy as a AAA platformer that's just a bit rough around the edges because it's extraordinarily overly ambitious, I can, however, forgive most of this because the game was just incredibly engrossing and compelled me to keep playing it. With all of that said, aside from the bad camera issues and minor delay in the combat I wish the music was a tad more memorable. The tunes are good but they aren't catchy, even though the voice acting is excellent and it's incredibly impressive that such primitive graphics managed to pull off highly accurate lip synching.
If the concept interests you, there's no question that you should play it.