SonicGMI (Generations Mod Installer) is the only mod manager for Sonic Generations, and is required by all mods.
You can download it here.
The Unleashed Project Mod comes with Sonic Unleashed day stages ported from the Xbox 360 version with many graphical and minor gameplay improvements, as well as its own hub world.
Sonic Generations renders generic shadows at 90° angles. This mod enables true directional shadows, lightshafts, and includes various graphical tweaks explained in the video. Note that the folder "Graphics Overhaul" is the main mod for the base game, while the included folders are intended to be merged with the mods named.
There's a way to go beyond the shadow resolution options offered by the game, and it involves some manual modifications to the executable. Step-by-step instructions can be found here.
Do not manually edit this file, use the configuration tool.
NVIDIA GeForce GT 555M
Save the edited file. You should now be able to play the game.
Download and install the Microsoft .NET Framework 4.
See Sound problems (cracking, delays, missing music/effects, etc.)
The detected configuration does not match your current hardware. Please run the configuration tool.
Go to Catalyst Control Center / Nvidia Control Panel and disable all custom Anti Aliasing profiles (reset it to default if needed).