I've played about an hour of the demo and a good 2-3 hours of the full Japanese version so i though that it would be a good time to write down my first impressions of the game. 
 
First of I'll have to say that the game looks stunning, not only the graphics but especially the animations of the "monsters". I use quotes for monsters because the quality of the animations make them look like actual existing animals. It is kind of odd the universe of a game called "Monster Hunter" would strike me as feeling realistic. 
 
Now  you are probably thinking what is realistic about a game with gigantic swords? Well the weapons have a sense of weight to them, characters struggle to move when holding them and appear to run no faster then a actual person would run (they are mighty good at swimming though). The human characters actually are proportioned humanly and don't have tiny waist and huge breasts which struck me as extremely odd when i saw it because you don't see that all that often in video games.
 
Character creation i must say was disappointing. Monster Hunter Tri has a really strong multiplayer valour so in that context you would expect a robust character creation system with some sliders here and there however the game only offers the minimal. There are a certain number of set faces but you can't create your own, hairstyles are not all them numerous either and you can't alter your size or body proportions. This all might sound a bit nit-picky especially since the armour will cover up your character but it is just a thing that feels weird.  
 
Controls feel fine, you'll probably want to use a classic controller to play it though since the controls feel a quite uncomfortable especially going from the D-pad to the 2 button to access the menus. The wii-remote+nun-chuck controls have the problems of having the + button and shaking the Wii remote do the same thing and it happened to me to accidentally "shake" the wii remote which would draw my spear. I suppose that you could turn this out in the menus, i hope at least because such a thing could probably get you killed in the later more dangerous battles. Another gripe i have with the wii-remote controls is that it does not use the pointer for the bow gun, at least not in the demo. Capcom have a certain game called Resident Evil 4 under their belt which has great aiming controls that would in my opinion be perfect for the bow-gun but alas to my knowledge it is not. 
 
Like i mentioned before Monster Hunter Tri has a huge online focus and that is something that unfortunately shows when you are playing it solo. For example there is a 20 second counter when you finish a quest so that you can wave and do emotes towards the other players but this 20 seconds wait is still there when playing the game solo which is a bit silly. 
 
I've enjoyed what I've played from it but I'm sure that the game would be way more enjoyable when playing it with a full 4 person party. Looking forward to the English release.

Slight update here. I've played 4 hours of the main game and i've got past the early tutorial escque section. 

This game has a really odd structure and i can't really say that it is fun playing it alone. The quest where you have to hunt monsters are fine but those that you have to collect items are a pain. The second quest you can pick up for example asks you to collect two horns of the gazelle like creature that wanders around however these horns have a random drop rate that is insanely low. I had to spend 30 minutes poking these creatures with my lance before i even got one and then before i had the luck to get the second one the timer ran out. I'm under the impression that i might have done something wrong because the subquest was to kill 5 of them and in the end i must have killed around 50. Anyway it is just no fun. 

I'm pretty close to saying that this game is not worth the hassle if you are playing it solo. I really hope that Capcom makes the right descion and does not force a subscription fee for the online in Europe and the US like they are doing in Japan because if they do i doubt that this game will take of. 

I had Monster Hunter : Freedom on psp , as did a few friends of mine . I can honestly say , solo the game holds its own , but making a hunting party with friends and killing Huge Leviathan Bosses is simply one of the best co op experiences ive ever had . Just my two cents :)