I would call it Generations 0.5. The controls for Modern Sonic and Classic Sonic seem worse than Generations. Modern Sonic's stages have been oversimplified. For example, there are fewer alternate paths that the player can explore to find the quickest one, so it does not have the same replay value that Generations, Unleashed's day stages, and to a lesser degree Colors had with regards to replayability for speed runnning. There is very little with regards to enemy variety. The trick system to build up boost is gone. Drifting is gone, which further contributes to the overly linear 3D level design. Very few bosses and the Infinite bosses get very repetative. It is not terrible (like Rise of Lyric or Sonic 06), and I am having fun with it but not as much as I did with Generations, Unleashed mod for Generations (plus Unleashed's original day bosses), or Colors. 

I feel Unleashed and Generations suffered because Sonic Team insisted to putting to different gameplay styles into a single project. As such for Unleashed, the warehog stages overall felt really unbalanced and broken and the day stages had control issues (largely fixed by the fan Unleashed mod). Generations felt short with regards to lack of more classic Sonic and modern Sonic stages. Forces which incorporates three different gameplay styles feels and plays notably worse. The sad thing is that I like all three of the gameplay styles in Forces, they just all seem to be unrefined because Sonic Team tried to simultaniosly throw them all into a single game. Three dfferent games, each getting Sonic Team's full attention, would have had a much better chance of being of higher quality than the single game we ended up getting here.

Its the number 1 selling point. Over 500 items. 

Never trust Sonic Fans. Actually never trust User Reviews on metacritic period.