It`s not MMO-anything.
Think of monster hunter as "bite sized PSO"
levels CANNOT last more that 40 minutes (if i recall correctly) as that is the maximum time limit impossed, and in reality, with a party of 4, it`s usually all over in 10 minutes.
That is what is so great about MH - you can drop in, slaughter some animals, then leave. No massive night long commitments to doing one quest. If it`s a night long session, then you are going to be doing lots and lots of quests.
HDD support - NO. Just a BBA is required.
Cheating - i`m sure someone can hack the mem card to give you the items you need or whatever, but cheating seems to be at a minimum. The Rare-item thing works really well - apparently , there is a loop hole that allows you to replocate sub Rare-3 items. But this is basically crap like mushrooms etc that sell for next to zero money. And in any case, cash is useless without the rare-4 / rare-5 items. These items are usually parts of the bigger monsters, and are used to create new weaponry and armour. You have to EARN these. Players cannot trade Rare-3 and above items, so if anyone has a certain blade or a certain armour then basically they had to go through the process of killing whatever they had to get the parts.