Pretty self explanatory.

Explain to me why I should be excited about hunting monsters with people online.  Don't get me wrong, the graphics look good and from everything I hear about the game it's supposed to play great, but I'm not sure if hunting monsters sounds like it'd be that much fun to me. 

Am I missing something?  What makes this an awesome must have game?

who doesn't want to Hunt big Giant Monsters and play a 300 - 500+ hour game lol

and plus the Online is suppose to be Massive

If you don't you are a poopyhead

The big monsters are not something you just take down. You have to prepare well and learn the monsters traits and tells in order to take it down. All the big monsters come as challenges, and all of these are passed because of your own skills. It's not about grinding, it's about learning and knowing that the rush you get from finally defeating one of these monsters comes because you mastered it and not because the game let up, or because you earned enough XP or whatever.

Doing so online in groups means bigger prey, bigger challenges and bigger rewards.

Okay... Basically, I think that the best reason for you to buy this game is the multiplayer.
I take a course in Interactive Games Development meaning I have played tons of games from all genres etc etc.
I have never had so much fun on Monster Hunter like I have with other games. It's a fantastic experience, taking down a huge incredibly difficult monster with all your mates. And then after, seeing each other in the real world and saying stuff like 'Aww man you did great lastnight' or... 'I've finally got the armour!' and then everyone marveling over how awesome you look.
Monster Hunter is not very competitive at all, it is ALL team based. Even when you are alone you have help from your trusty Cha Cha (A companion in the game that helps you hunt monsters)

I think the reason why I love it so much is I'm not into competitive games at all, I would prefer working in a team.

Best thing to do is just get it, if you don't like it; fair enough, trade it in.
:D

The feeling of satisfaction every time you complete a hard,one hour long quest with your friends.
You must try it at least once to understand what I mean and how it feels.

It sounds like the type of game that you have to actually play to understand, am I right?

Also, would I really be a poopy head if I don't get it?

That's what I've heard, I haven't actually played it though

The reason I'm really hyped about it is because it reminds me of Guild Wars. It's not your level that determines the outcome, it's the preparations you make and your own skill and judgement. Of course in Guild Wars, it was all about what skills you chose to bring with you, and little about equipment, whereas in Monster Hunter, it's exactly the opposite, but it's still the same principle.

On that point, why don't you just get the demo? That would be the best way to decide.

We don't even get that sort of promo service in the UK.