MH3 is a stripped down RPG, but it's simplicity and difficulty is part of what makes it fun.
From the couple of evenings I've plugged into this game, I can tell you that this game is not for the faint of heart. Most gamers will probably be turned off by the game, considering it's an RPG with no spells, no mega-hotties, no story, no real leveling system, no talents, and no giant robots.
However, its simplicity is also what makes it charming and difficult. It reminds me of playing Poker. The rules to the game aren't particularly difficult to comprehend (you run around smashing monsters and harvesting goods to get better gear to kill bigger monsters). However, this is NOT a game you can hack and smash your way through. There's a lot of grinding materials for gear (a la World of Warcraft), and when you are faced with a larger monster to slay, the fight can take up to 45 minutes to bring him down. This is NOT 45 minutes of tapping the A button until its health eventually depletes. This is 45 minutes of active dodging, shielding, and timing perfect hits while a massive dinosaur shoots lightning bolts and summons minions to destroy you. If a game that's basically is a series of hellish end-game bosses appeals to you, this is your perfect game.
Most RPGs I play, I notice that I stockpile reagents and potions, because I'm never really faced with a fight difficult enough to use them all (I tend to grind levels so I outlevel whatever I'm facing). This is not a game you can that. Partially because there isn't any XP. Finishing quests will unlock harder quests, and that's about it. The only way to truly progress is to up your gear and up the monsters you kill.
The story to the game is almost non-existent. That's not to say it's completely barren of characters. There were a few lines of dialogue with the Guild correspondent that have made me smirk and there are a handful of vendors (including walking, talking cats) to interact with throughout the game. Plot-wise, there's almost nothing. You get a few lines of text explaining why the village needs you to kill monsters, and then you're sent on your way. If you enjoy RPGs that have cut-scenes after every battle and a very dramatic story line, this probably isn't for you.
Music: there isn't really anything playing the background while you run around the wilderness. You'll get used to the sound of the wind and your feet and some monsters growling at you in the distance. You'll grow to appreciate this, as it'll make it more obvious when something is coming from behind to devour you.
Graphics: Great monster design. As typical with the Wii, the actual graphics look a little fuzzy and untextured, but by Wii standards, they're pretty damn good. The armor and weapons are well-designed, and for the most part, just look really cool. They also did a good job with your character customization options. You can choose from dozens of hair styles, faces, and voices for your character.
Multiplayer: The game allows you to play with up to four people at one time. You can trade in-game codes with friends to meet up in-game, or you can pick a random room to play in. There's various rooms labeled for specific playing goals: ie, if you're looking for people to quest with or meet players who are new/experienced. It can be a little clunky to figure out who and how to disembark on quests with other people, but with a little patience you get the hang of it eventually.
The too-lazy, didn't read version:
A good game if:
-You're a fan of the series already.
-You're looking for something with a very high level of difficulty.
-You enjoy micro-managing characters: picking the right weapon for a specific fight, having multiple sets of gear, having the perfect upgrades, traps, etc.
-You have a lot of spare time to devote.
-Will provide a lot of hours of play.
-Decent online.
-You'll actually feel like you've achieved something great when you down a big monster.
-The game's tutorial is clear and easy to understand. I would recommend starting in Single player mode, because it was a lot more overwhelming to start in Online. Overall, it gave good instructions on how to get materials and use them.
A caution:
-NOT a game for casual players. This game requires time and effort to be successful.
-Difficulty may be too high/frustrating for a lot of players. Weapons are slow and require timing and precision to land a successful hit. Patience is a requirement.
-There's no spells or talent points, which will turn off a lot of RPG players.
-No auto-targeting. Expect to miss. A lot. A pleasant challenge for those that don't want their hands held, an annoyance for others.
-Potions/reagents can be tedious and frustrating to use. Instead of just eating it and gaining the benefits immediately, it'll do a little animation that will give any monsters in the area enough time to catch up to you and smash you. More likely than not, you'll have to leave the area to successfully eat an herb/potion, which can be more annoying than anything.
-This can also make harvesting monsters annoying. You'll get about 30 seconds to harvest a monster after killing it before it fades away. If there's a lot of monsters in the area, they will make it almost impossible to successfully harvest a monster. This is either another challenge or a turn-off for others.
-This game is not well-designed for the Wii controller. Most people I know picked up the classic controller for this game, just because it's too clunky with a standard controller.
-It's designed to open-world, but a map is really a very (very) small region linked to other regions via load screens. The load screens are only about 2 seconds long, but it makes the game feel linear instead of open world.
Would recommend if you like:
World of Warcraft, Pokemon, classic RPGs