Definitely not an RPG.

Wikipeida says it's "hack-and-slash, adventure, and strategy" which pretty much sums it up.

Basically, there is no leveling system, aside from your Hunter Rank. Your Hunter rank goes up after you compete a set of quests, which consist of gathering quests (finding a certain amount of an item), Slaying quests (killing a certain number of weak monsters) and Hunting quests (Killing a certain monster, usually, very strong, thus where the strategy comes in). Defeating the big monsters is a huge undertaking. You must plan for it immensely. If it's a hot environment, bring cold drinks so that your health doesn't deplete, and vice versa. Bring Sonic bombs if it's an underground creature, so that the sound can make it come to the surface so that you can attack it. Bringing traps, so that you can trap it to capture it, or take a few swipes without it killing you. Then you choose what weapon to use, longswords, greatswords, guns, bowguns, dual swords, hunting horns, gun lances, and a few I can't remember. There's an immense layer of strategy that goes into even the simplest missions, since you never know which mosnters that you will encounter.

It's a VERY niche game. But if you like it, it's awesome.

That's the shortest way that I can sum-up Monster Hunter, but I've cut a lot of corners, and over-simplified everything, which MH doesn't do.