tl;dr: A really enjoyable modern take on the 2000s era 3D action/platformer without the mechanical hang ups or technical limitations of games made in the 2000s. Big thumbs up, highly recommend if that genre is one you enjoy. You don't need to play the first Psychonauts to understand what's going on in this game, but it might be worth trying the original for $1 if you feel like it.
Old Friends
Psychonauts 2 does a great job preserving and updating what was special about the previous Psychonauts game. It captures the essence of the-way-you-remember-this-kind-of-game-feeling-back-in-2004 to a T; the premise is wild and over the top, the classic Double Fine writing style makes the dialogue and jokes mostly fun (only a few overstay their welcome), the characters are very visually distinct and the environments are absolutely gorgeous, and on top of it all the platforming feels snappy and responsive. These core elements executed with modern sensibilities and technologies in mind make for a baseline of a fantastic to look at and buttery smooth to control game.
Older Enemies
More important though than what it preserves from the 2000s era games is what it discards. Many of the 3D action/platformer titles from that time liked to gate the next level or the next weapon behind an arbitrary limit of collectibles collected. In the more lenient cases that could mean revisiting a level or two to find the missing pieces while the more egregious offenders (I'm looking at you, OG Psychonauts) might require you to revisit a large number of the levels you've already completed to scour them for a handful of well-hidden collectibles before allowing further progress. If you have the time and patience for that, then no skin off your back for the several hours of thorough collecting you would have ahead of you. But if you are a typical adult with typical adult responsibilities, you probably lack either the time, the patience, or both of those qualities with regard to lengthy required backtracking. But remember this is Psychonauts 2 we're talking about here, not the original, and Psychonauts 2 understands that asking the player to repeatedly revisit significant chunks of the game is a prime way to annoy people away from the game.
Collectibles in Psychonauts 2 are -- mercifully -- optional. You can, with sufficient skill in the combat mechanics, happily play through the whole story without even thinking about going out of your way to pick up a collectible. That's not to say that you would be likely to enjoy your time fighting through the harder enemies without upgrades from collectibles, but getting a reasonable set of upgrades happens naturally as you explore the overworld and individual levels. If at any point you do find that you've overextended yourself however and combat becomes more difficult than you would like, you are always able to choose to revisit previous levels and collect more upgrades to remedy the difficulty. Regardless of what collection strategy you choose though, you will never be stopped by an artificial barrier in the game demanding that you go collect 200 more dinglehoppers or 3 more hidden sporks before you can advance to the next level. Psychonauts 2 is perfectly happy to let you experience everything it has to offer in one go from start to finish.
Runtime
With that said, "everything Psychonauts 2 has to offer" does not go on all that long. I managed to complete the main story of the game in about 21-23 hours and spent another 4-6 hours revisiting the entire game to clean up all remaining collectibles and missions for a total 100% playtime of ~27 hours. For what Psychonauts 2 sets out to do and for the story it tells, I think 20 hours is a very reasonable runtime. It certainly could have been made longer or had DLC added, but I think it very neatly accomplishes what it claims to do: tells an entertaining story through beautiful levels, customizable combat, and snappy platforming, all while cleverly avoiding 2000s era gameplay traps.