Well the PSP version is the most fun on a handheld I've had since... Mario Kart DS D= Oh snap!

There's tendency in game development that I personally call 'over-featurization', i.e. let's take existing and highly popular formula (in this case - arcade kart racing) and put a lot of features in it (track and characters editing, kart moding etc.) so we could easily promote this game as superior experience of it's own kind regardless of how good is core experience. Actually it's the same story with pretty much every 'killer', that's how industry works - throw in competing product in every opponent with successful franchise. Surprising waste of own talent.

Yes, games are good on their own merit. No matter what MNR does, MK will always be good. I am not saying that MK sucks just because another game might be better. I am not looking to rile up others, but the two games should be compared because they are in the same genre. By killer, i mean a game that will step it up, above what MK has done.

In terms of sales it won't kill Mario Kart, not even close

But in quality and innovation I can see it beating Mario Kart

I'm not even going to give this game chance. Little Big Planet was by far the biggest disappointment for me this generation, so I wont bother with this thing!!

This looks SOOOOOOOO fun I love arcade style racing games...plus the play create share mechanic is amazing...I mean upload your car, have others try it, rate it and even modify it. Pretty impressive...plus the track creation/modifying looks pretty great as well. Lots of creativity...

It won't do nearly as well as Mario Kart Wii because...well lets face it Mario is just too popular but I'm sure it will appear to the younger audience PS3 owners, and plus this seems like a good split screen party game, assuming it goes up to 4 players?

NOPE! It isn't a Mario Kart Killer. One hopes that it does its own thing though, and ends up doing real well. It looks great from what I had seen of it. I do hope that new modes arise, akin to Grifball in Halo.

CAN'T WAIT!!!

does not look as "pick-up-and-play" as MK
that said, perhaps most won't delve too deeply into the complicated aspects of MNR and just thrash around with a few mates
so, judgement reserved until I've played it

Nope.  It's going to kill Mario Kart badly in gameplay.  It's a shame that I only own a Wii and have to play that piece of crap known as Mario Kart.

Mario was killed in this way by Sackboy too.  It's such a shame...