And, so far...
The game camera looked annoying, it's not a 'smart' camera - you have to position it yourself. Time will tell if it's an irritant.
Some of the characters look a little basic too - un-textured and just gourard shaded :(
Some of the textures look (at times) very lo-resolution, which considering the GC's texture compression (5:1, if memory serves) is a touch disappointing.
I've saved (IMO) the worst 'til last... the water effects.
Not the sea/ lakes etc, they're lovely.
I'm talking about the 'water-on-floor' effect from the water-spraying backpack. There's no splash effect when the water hits the floor, all that happens it a transparent circular poly that shrinks over time. It's flat, has no sparkle and looks quite amaturish (although it does reflect Mario when he runs thru it).
It just looks weak compared to the other water effects in the game.
The 'warp' effect is quite nice too - Mario gets broken up into a load of coloured ball sprites that fly into graffitti on a wall, fade to black (or whatever) and reforms on the other side. Nice.
It seems to play, well, exactly like Mario64 with a backpack... if that's your cup 'o tea, you'll love it.
Me? I never finished Mario64 - I got stuck (and a little bored because of that)
When I see a bit more of it, I'll let you know what else I think :)