Apparently a LOT.

As a Monster Hunter player since it’s first incarnation on the Ps2 and it’s iterations on the PSP, I can say I’m really excited for Monster Hunter Tri on the Wii.  Aside from radically different control scheme, the upcoming (or already release if you’re referring to the Japanese version), Tri offers a whole new different world filled with new maps, new equipments, new moves and of course, new and powerful monsters!  I’ve been looking at several videos of Monster Hunter Tri and I must say, I’m really quite excited about the game’s release.
Since there’s quite a LOT of things new and updated in Monster Hunter Tri, I’m not about to post every single video I see on the net but tThe video below seems like a very good summary of showing what’s new in the game.

I’ll try to enumerate the differences from P2G from the video above:

• Overhauled Graphics.  For a wii game, it’s definitely something to see.
• A much larger area (or dungeon if you’re an avid RPG fan)
• New attacks (The great sword seems to have an additional charge attack and two other moves)
• Monsters can maul you now (I think this is in another vid)
• A hit from wyvern fireball seems like it has a burn status (you can see the embers on the armor after getting hit by a fireball)
• Battles are more chaotic (there was a scene were about five monsters were attacking at a time)
• Gameplay is much faster (maybe that’s just me)

As for the additions from other videos (you can view the official trailer and the control demo here.

• A new pet – a shakalala (for underwater battles, felynes can’t swim )
• A new weapon – the slash axe
• New areas (like underwater)
• New monsters (every new MH title ups it’s monster catalog so no surprise ther)
• New attachments for the bowguns
• COOP Multiplayer split screen (I think this is for playing with 2 players on one Wii)
• Online Multiplayer (no details though but there’s rumor that it’s going to be a paid system)

I’ll add more once I get my wits about me.  There’s simply too much stuff that it’s hard to filter Capcom has really out done itself with Monster Hunter Tri.

Even from just seeing the videos however, I can see how intense Tri is. If you think Freedom Unite is hard, you’ll probably end up hating Tri. The US/EU version for Monster Hunter Tri has been confirmed for 2010. Note: post seems very cluttered.  I’ll polish it once my wits are about me.