As someone that has played (and loved) many of the Sonic the Hedgehog games, it has become quite clear that the quality of Sonic games have deteriorated greatly since its roots. Just look at the mediocre reviews of Sonic Lost World and the pretty miserable scores Sonic Boom has received. What happened, Sonic Team?
However, out of the most unpopular Sonic games (Sonic '06, Shadow the Hedgehog, Sonic R) I have to say I don't hate "Modern Sonic" games. Everyone wants Sonic to go back to the sidescrolling 2D game genre. I am a minority legacy Sonic fan, in the sense that I loved many of his 3D adventures and would claim that they're good enough to be numbered among the Sonic 2s and Sonic CDs.
A great example of this would be Sonic Generations. Fantastic game! I find myself playing the 3D levels MUCH more than the 2D ones, but even the 3D zones incorporate elements of the 2D style of gameplay. I feel like if SEGA stuck with this style of genre, their games would do very well. Imagine...Sonic Unleashed minus the werehog levels! The daytime levels in that game were incredible. Why can't we see more of that style in more new Sonic games?
If SEGA would just release a true Sonic Adventure 2 successor...say a, oh I don't know, Sonic Adventure 3 (did you read that, SEGA? Go ahead and go over the bold part a few more times. Sounnddddssss like a good ideeaaaaaaaa, doesn't itttttttttttttt??), that game would sell like hotcakes. Plenty of people feel nostalgia toward the Sonic Adventure series, and let's face it, a more polished version of Sonic '06 could have been really good.
Also, they should actually finish the game and not keep letting it be buggy and not ready for release.
Also, people look to Sonic Heroes as the beginning of the downfall of Sonic, but I loved that game. I also loved Shadow the Hedgehog, and actually played through all of Sonic '06...so maybe I'm not a credible source. Anyone who's done that has got to be a fanboy.
I guess, if you were to think of a way for SEGA to "fix" Sonic, what ideas would you have, readers? You can only combine speed and platforming in a 3D environment in so many ways. I'd love to hear your thoughts.
So TL;DR version: SEGA should make more Sonic Unleashed (DAYTIME levels)/Sonic Generations-styled Sonic games and include elements from the Sonic Adventure story and use an overworld. This would mix the exciting modern Sonic gameplay while incorporating elements of the 2D Sonic games that everyone loves (high-speed platforming) and the storyline from the Adventure games with which people can identify.