Me and my friend were talking about how they keep trying to do Sonic in 3D and missing the mark. Unleashed nearly got it but messed up with the werehog part, which could have been ok if it wasn't for the Crash Bandicoot style play. But Sonic is about speed... Speed, collecting rings and jumping on robotic bad guys. We got to talking about what we would like to see in a sonic game and, inspired by the Sonic CD intro, this is what we came up with;
They should make a Sonic game with a massive freeroam world (like Assassins Creed, GTA or Zelda) instead of a restrictive/on rails game. It should take a 3rd person view, maybe switching to side scrolling at certain points but there shouldn't be lots and lots of obstacles so as to not take away from the running and speed you could potentially build up.
The world could be based on Emerald Hill zone with all its lush greeness, loop di loops, bridges and floating platforms, which could act as your starting point and general 'free play' area and then it could also comprise different regions that match some of the old zones such as Sandopolis, Ice Cap, Aquatic Ruin, Lava Reef etc. and no set path or order so you can zoom in and out of each area where and however you want. They could have a water area that you have to build up enough speed to run across (similar to Dash in Incredibles).
There could be certain tasks to complete within each area, certain checkpoints to reach and a certain amount of rings to collect. Each area could have its own special stage (and take it back to Sonic 2 style special stages) and it's own boss.. although instead of been Robotnik each time, it could be a series of different robotic henchmen.
There could even be optional side quests to complete such as races to compete in, objects to collect, characters to save. You could get acheivments for the amount of animals you free from robotic forms or the ammount of rings you collect..
The overall story should go back to it's roots with the idea of sonic collecting the chaos emeralds to stop Dr Robotnik (not Eggman) taking over Angel Isle. But it could also borrow from the slightly more edgy mid 90's Sonic cartoon with ideas like Robotnik capturing the inhabitants and robotising them for sonic to save. Maybe even include Metal Sonic. Maybe Robotnik built Metal Sonic to find the chaos emeralds, so your racing against him to find them all.
But there could be a different chaos emerald hidden within each region.. Like the region based on Ice Cap could be a big snow topped mountain looming in the distance. It could switch to a vertical run up the side on the moutain, dodging avalances and stuff, where the emerald is waiting at the top (maybe even do this side scroll style). There could be an emerald hidden within a dark pyramid (ala Sandoplis Zone).. This way there could also be a lot of variety between areas and with no set path or order to collect the emeralds in you could go to each zone in any order you like.
I don't know how or if they could do this but maybe introduce a time limit to find each emerald. If you don't find it by the time is out then Metal Sonic gets it before you. So potentially Robotnik could end up with more emeralds than you which could either loose you the game or give Robotnik the advantage in the final fight.
Perhaps even introduce the idea of actually collecting rings for a reason.. the more rings you collect, the faster you can go. Maybe going a bit further and developing the idea of momentum and 'brakeing'. Push the trigger forward to go faster and pull back to start slowing down.. Imagine if they had a water area you were running across but you hit something or start slowing down and without the momentum sonic would sink into an aquatic zone like world. Or with enough momentum Sonic could springboard great distances or run up walls...
There should be no human characters except Dr Robotnik obviously.. Minor characters such as Amy could be included but shouldn't interfere too much with the overall game but don't bother with Shadow or Silver. Knuckles and Tails should be included and have a fairly substancial part, perhaps even switching characters to reach certain areas (similar to Sonic and Knuckles or Tails been able to fly you in Sonic 3).
But I mean.. just imagine speeding though a giant open world going wherever you want and doing whatever you want and watching it physically change around you as you travel through each area.. *drools*