I will go ahead and assume you mean RPG’s. I haven’t played Monster Hunter and I don’t know what you’d like, but I highly recommend Strat RPG’s. There’s a couple really good ones out:
Disgaea- The plot is funny (and roughly 20-30 hours), and if you have the patience for it, making perfect builds of characters can take upwards 100+++ hours. Plus, there’s plenty to do outside of the plot. If you played the PS2 version, it’s slightly better, and has multiplayer.
Final Fantasy Tactics- It’s a bit shorter, but there’s a lot more you can do with fewer characters. I’d say you can do the main plot in 10-20 hours, and make your character perfect within 50-100 hours. It’s quite an upgrade from the PS1 version. Some of the terms are changed, and it also boasts an addictive multiplayer mode.
In other notes, I’ve heard Crisis Core and some other Square Enix PSP games are good. If all else fails, you could always just buy a DS and play Pokémon.