Tbh, I'm not fixing really "bad games" but here's everything anyways.
I'd make Sonic Blast and Ladybirth never exist.
I'll give 06 more development time.
And then, make a PC port for Unleashed and then allow a little creator-thing for SuperStars and Frontiers (basically a thing where people can make abunch of cool things like levels, new textures, and other things that is already within the game.).
Then make Sonic Heroes, and STH for GC, & OG Xbox only, regradless of the PlayStation getting mad about no Sonic games on their console.
Throw the Wii U games deal into the garbage can, along with Sonic Boom.
Give Forces a longer development time, and make it have better animations and comedy.
And then add a better LEGO DLC to SuperStars.
And then make a collection for SA1, SA2, & Heroes that includes them remastered.
And then port a Rated T version of Shadow the Hedgehog that makes the game better then ever!
And give Sonic Colors Ultimate longer development time.