Ok, so if all goes to plan - I'll be getting a 360 (my mates he is selling to me - with a 6-12 month warranty) on the weekend.

I get to choose two of his games as part of the package - I don't know exactly which ones he has yet (he does have Mass Effect, and I will be getting that).

...

What games should I be looking out for, and which shouldn't I?

 - I like adventure/RPG/platformers titles

 - I dislike racers, shooters/FPS titles, "grunt" action games

If I had to choose between Oblivion, Lost Odyssey or Eternal Sonata - which should I get? I tend to prefer "harder core" RPGs (harder ones for sure). I might be able to grab one, and borrow a couple of others.

Is Assassins Creed worth it? (or am I better off borrowing it, or renting it?) - not sure if he has it anyway.

Some of these have been released:

Banjo Kazooie(Platformer)
Eternal Sonata(RPG; 1st)
Lost Odyssey(RPG 2nd)
Oblivion(RPG, 3rd)
Infinite Undiscovery(RPG)
Tales of Vesperia(AAA RPG)
Assasin's Creed: Personally liked the freedom, but it was very repetitive.
FFXIII(RPG)
Star Ocean 4(RPG)
Bionic Commando Rearmed(Platformer)
Braid(Platformer)
Last Remnant(RPG)
Fallout 3(Action RPG)
Fable II(Action RPG)
Too Human(Action RPG)
Castlevania( Platformer RPG)
Ninja Gaiden II(May be a bit too "Grunt" action, but absolutely amazing)
Devil May Cry 4( Action)

These are just some. Hope they help.

theres a "Games to Buy" thread by stickball thats stickied in the MS forum....im pretty sure you can just look there

BIOSHOCK

Assasins creed is worth it , will take you more than a few days to discover everything so best to buy it 2nd hand then just sell it on at a later date..... in terms of platformers..... if you never played it back in the day then Origional N64 version of Banjo and Kazooie is coming to xbox live arcade soon.... (Banjo scored huge and is still as good as any of the modern platformers out there if not better).........

Of the RPG's you listed I've only played Lost Odyssey, but it doesn't disappoint.

Lost Odyssey is surprsingly good. The story is fairly good and the combat system is amazing. I say get it out of the three you listed.

If u hate shooters, ur missing out on "Halo 3" and "Gears of War"

Otherwise, GTA4 is a mix shooter/adventure
Elder Scrolls 4 is a very nice RPG, I would get that

Fable 2 and Fallout 3 are coming out in a few months, I'd pick those up.

Dead Rising!

I'd get eternal sonata, but Lost Odyssey is also a good choice. Pick the one that targets you more.