Unless I obtained a different version than the final build... here's a mini review.
The game starts you off on Splash Hill Zone 1, an accurate recreation of Green Hill Zone, with a few more jump pads. After beating the first stage, you are put on the main menu, where you can select acts 1-3 on Splash Hill, Casino Street, Lost Labyrinth, and Mad Gear Zones (boss battles aren't unlocked until all three acts are beat). After entering your first special stage, you can also pick through levels 1-7 as you unlock them. Although the game is essentially "Run right until you hit something" two modes are available for leaderboard score whoring: Score Attack and Time Attack. I'm not a big fan of the graphics, they're very Sonic 3D Blast-y with a little less gloss. I'd poop myself a little if a throwback sprite Sonic was unlockable at some point...
The controls are simple, as they should be if it's really going to be a sequel to the originals.
The control stick feels kind of iffy, and I hate the 360's D-pad enough as it is. The homing attacks from the Adventure/Rush series (for me) are an unwanted addition, but will enable you to find alternative paths, extra lives and what-have-you.
The key element in every Sonic game is speed, and the Genesis titles seem to have pulled that off better than any crap Sonic Team can come up with. The layout of SPLASH HILL and CASINO STREET are nostalgia bombs, taking almost completely after the stages from Sonic 2 with a few renovations for the homing attack, ziplines swinging vines and the various spring pads. Thankfully there's no grinding that I've seen so far.)
100 Rings is an extra life. Seven Chaos Emeralds and 50 Rings makes you Super Sonic; unsure about ringburn.
Bubble Shield - Take one hit without losing any rings, or dying without rings. Falling of the map (and drowning?) can still kill you.
Invincibility - Automatically kills enemies by touching them, unaffected by spikes, and any hazards other than falling off the map.
Running Shoes - Gives Sonic a temporary (about 30 second) boost of speed.
Extra Life - Adds one life to the counter.
of course you know these already. Thought i'd add it in case something new pops up.
The Story Begins (5g)
Clear SPLASH HILL ZONE, ACT 1.
The First Chaos Emerald (5g)
Acquire a Chaos Emerald.
Crush Dr. Eggman (5g)
Defeat a boss for the first time.
Enemy Hunter (10g)
Defeat 1,000 enemies.
Golden Flash (10g)
Clear all Acts as Super Sonic
All Stages Cleared! (10g)
Defeat the final boss and view the ending.
Upload your recorded scores and clear times for all stages.
Ring Collector (15g)
Collect all the Rings in 'Special Stage 1' and Clear the stage.
Build up 99 or more extra lives.
Super Sonic Genesis (30g)
Acquire all seven Chaos Emeralds.
Speed's My Game (35g)
Clear SPLASH HILL ZONE ACT 1 in less than a minute.
Clear the E.G.G. STATION ZONE without taking any damage.