In PSO you gain experience, if nothing else, for every kill. That means each kill contributes to a level up, level ups make you stronger, so character strength is directly tied to how much you kill. In Monster Hunter you get nothing for killing something in game. In real life you learn a bit about how to kill the monster and thus can hopefully do better next time, but your character in game gains nothing.
In PSO gear can literally limit you. If you aren't strong enough you will do ZERO damage to things. In Monster Hunter you will always do at least some damage and you can kill end game things efficiently even with mid game weapons if you're good enough.
In PSO the best stuff is gained by super luck. I mean the odds of the best gear dropping is so low you can go your whole life without seeing it. The difficulty to obtain the best gear is time. It's not if you kill the boss, it's if the boss drops the loot you want. In Monster Hunter even the rarest drops are super common in comparison. The hurdle to overcome for the end game isn't if you get the drop, it's if you can kill the monster.
In PSO, class determines your weapon. In Monster Hunter, your weapon choice determines your class. No choices at character creation limit you in any way later in the game (with the exception of very few gender specific armor sets).
In PSO you need to kill everything to leave the room. In Monster Hunter no paths are ever blocked (with the small exception of during the first tutorials) and you rarely want to kill everything you see.
I got this game like 3 weeks ago and after playing it, it constantly reminds me of PSO.
You progress through areas with increasing difficulty. Each area had its own ecology. You fight in groups of 4. The Shakalakas are like MAGs.
There is a sense of exploration and wonder. The main point of the game is fighting monsters to collect loot and get rare weapons and armor. The Banabras remind me of the Moth things and and robot buzzers in PSO. Once you rank up, new species are introduced just like in Ultimate difficulty in PSO.
When I fought Rathian for the first time and also Rathalos I instancely thought of the PSO dragon fight under Central Dome. The Brachydos armor and weapons look similar to the D. Creatures and Dark Falz in the ruins.
I think MH is much better though. The gameplay is significantly better than 3 hit combos and the fights are bosses not swarms of small enemies. I think that is why I enjoy this game because I put hundreds of hours in PSO on both Dreamcast and Gamecube