Okay so is Monster Hunter basically just an action/adventure-semi-MMO thing like PSO, just killing big monsters and loot whoring online with people?
Or is there like an actual story mode and stuff?
There is a bit of story but it's usually incredibly fast paced and doesn't last you long.
The game itself is essentially a straight boss arena action RPG, most of the fun comes from either playing online with friends(or Randoms) and just grinding out monsters for parts to make armor/weapons to progress to harder monsters. In this you could call it an MMO but in my opinion it's not extensive enough for the word, it's very straight forward and grindy with a relatively tiny world. On top of this, while there is some "lore/backstory" behind the missions you do, it plays little into what you're doing to the point of you needing to honestly read little to no dialogue or even text in general.