It has real time collapsing objects, a relevant physics engine, expressive character models with a toon consistency to them, and high speed gameplay... among anything else I might have forgotten.
Most of that is pretty standard (with the exception of the physics engine,
which might be very good, although, knowing Sonic, I'm not expecting much).
Sonic Adventure had all that (especially the expressive characters... too expressive! :P).
There were many places where objects collapsed, one of them being Sky Deck 2,
where about a third of the Egg Carrier's wing broke up and fell.
And SA is 8 years older, plus it's on hardware that was already very
old and outdated even before the XBox 360 was released (and it was a launch game).
Oh, and again, there's a difference between physics and graphics.
F-Zero GX cars can look pretty good, but they're still quite simple. The tracks look good, but they're hardly ambitious. F-Zero GX gets away with looking good and being fast, but it was the least it can do considering the approach they took with the game.
It's not just "fast". You seem to be familiar with it, so you must know that
the machines can move at over 1000-3000 km/h, even when they aren't diving.
(The Space Dive trick would make that 9500+ km/h.)
And there's the size: roads hundreds of feet wide (a good part or
even most of an Action stage), "small" boost plates that are at least
60x25 feet, and pit lanes that could swallow long, narrow action stages whole.
F-Zero and Sonic can't be directly compared in graphic quality
(in detail and polygons) if the size and speed are so different.
Well isn't that expected? I thought it was with all games, not just Sonic06.
Exactly! I doubt that any of the three systems will
go more than half a generation ahead of the current ones.
Rolken blames it mostly on this game. I half-agree.
Sonic hasn't delivered good graphics since 2001, and this one
probably follows those more-recent games. Also, it probably follows
the original Sonic Adventure by relying on a new system to look good.
(SA was said to have good graphics just because it looked better than
what was already out (meaning N64 games, most of them still without
the Expansion Pak). It didn't use the system as efficiently as
some other games (I don't have a DC, so all I know is that SA looks
really bad compared to GCN, and I don't know about other DC games.), though.)
Mainly, I still blame it on this generation of systems just not being as
much of a step up as every other time since the NES or whenever.
Screenshots I've seen of Revolution (Wii) don't look much better.
They could have looked better, but I can't believe that they could look almost as good as Sonic06.
You agree with me at least on that the models in SA2B are
around the same smoothness as the models in Sonic06, right?
And even though SA2B mostly uses Dreamcast graphics (and doesn't
come close to pushing the GCN to its limits), some stages
(mainly non-metal stages) don't look that bad even on GameCube.
(On the other hand, the Kart racing stages and Sky Rail look pretty bad,
and the space stages are unimpressive, all of them partly because of pop-up.)
Metroid Prime doesn't have a lot of speed. The game also has the benefit of not having to display a character model 99 percent of the time. Also, most of the environments are tight indoor spaces, with many opportunities to load.
1. It's not that slow, and the Boost Ball is especially fast.
2. But it
can display the model at any place in the game.
You can press X repeatedly, and there's also an Action Replay code to
make Samus's model stay in front of the visor and cannon at all times.
3. Almost every game (some exceptions being platformers with wide-open
stages (the Mario games) and any non-racing sport I can think of)
does that, but MP gets off easy by having so many tunnels and corridors.
Other games have to hide the pop-up behind corners.
SA2 and Sonic Heroes obviously do this. I didn't notice anything in Sonic06,
(I only watched the video once), but it must be happening,
even if it's hidden perfectly (which it probably isn't).
It doesn't really count as a huge environment when pieces of it
appear and disappear all the time, and especially when the stages
are broken into areas with load times between them
(didn't you complain about that being in Sonic06 a while ago?).