How would you design a 3d Sonic game? Would you go more Modern style, Adventure style, a translation of the Classic style into 3d, or something different entirely?
Myself, I would go for classic-styled momentum-based gameplay in 3d, but with modern twists.
There would be multiple playable characters, playing in the same levels, completely optional, but with their own unique abilities ala 3&K. For example, if the playable cast of the game was Sonic, Tails, and Knux (Sonic is always a given because it's his damn series) Sonic would have speed and agility-based abilities, Tails would have his flight and tail attacks, and Knuckles would be able to break certain walls and be able to climb and glide. Which cast members were playable would depend of the plot of the game (which would have a balanced tone and be more complex ala SA1 or Unleashed).
All characters would share the spin jump, rolling, spindash, and some form of the drift (for example, a faster character such as Sonic or Shadow has the regluar drift, but slower characters such as Tails or Knux has a altered form of it that makes them lose speed when they do it). Base controls would be SA1's, but with twice the top speed (but no accel increase, therefore it takes twice as long to get there on flat ground). As you went faster, past SA1's max flat ground top speed, your turning radius, or "arc" would increase, like the Modern games.
The level design would be less linear, and paths would be less defined, making it feel more open. There would still be a strong sense of direction however. It also would be really slope-y, for lots of momentum-based speed ala the Classics. Basically what Dio has touched on before.
The pace would not be fast as Modern gameplay (to allow for more content), but you could still reach some pretty high speeds using momentum and such, and blur effects would be used at higher speeds to give a better sensation of speed.
Elemental shields would come back, as well as the speed shoes.
There would be hub worlds, and a turn-off-able arrow telling you where you need to go next, so there is no confusion, frustration, and bad scores from reviewers. Ala Unleashed, you can just select a level/act to play from a menu screen once you have beaten it.
If not this, then an improvement and expansion of Modern gameplay, because I love it and it's my favourite 3d gameplay so far. But as long as it's fun enough, I will most likely love it or at least like it, whatever style it is.
That's my take on all this. Thoughts? Discuss!