I've never played N+ on the 360, however I used to play the flash game version of N all the time, used to be a great way to kill the hours at school! Between some friends and I we unlocked about three quarters of the levels and colours on the game, and it was always good to solve the puzzles and work out the best ways to do it.

What I want to know is if there is anything much different between N+ and the original flash N game? Is it the exact same, or has it completely been updated? And is N+ exclusive to the X-Box 360?

N+ is exclusive to the Xbox Arcade. As far as I know there's more enemies in the Arcade version than there was in the Flash version. Not to mention the Creat-a-level function, online co op and tonnes of new levels, both co op and single player style.

I believe the create-a-level function was in the flash game as well, but there certainly wasn't any co-op! Now I want to get it! Any chance whatsoever that they'd multi-platform it?

it's out in NA for DS and PSP at least yeah

Mainly for handhelds, apparently.
Xbox must have struck lucky on this one.