Just to back my point up, I'm going to rank every main game post-Genesis, based on both my own opinion and critic reviews, and we'll see what the hit to miss ratio is.
Sonic Adventure: Critically acclaimed at the time, some say it hasn't aged well but most still seem to regard it as a good game. It's not my favorite, but I'd give it a solid 7/10. Hit
SA2: Also critically acclaimed, the HD release a few years ago was also well received. Easily one of my favorite games in the whole series. Hit
Heroes: The closest 3D Sonic has ever come to truly recapturing the spirit of the Genesis games. Critics loved it, but unfortunately it's never been rereleased so I have no idea what they would think of it now. In my book, it's second only to Sonic 3. Hit
06: A total disaster, and thanks to Game Grumps' memetic LP it became the launching point for all the "Sonic was never good" BS that still gets copypasted all over the internet. I enjoy it in the same sense that I like Jurassic Park Trespasser; it's such a train wreck that it's fascinating to experience firsthand. Miss
Unleashed: There are two totally different versions of this game. The version released for Xbox 360 and PS3 is very divisive, opinions are split down the middle about whether it was awful or a return to form. The Wii version got generally positive reviews, and it was this game that paved the way for the next few entries. IMO, the PS3/360 version is one of the worst games I have ever played and the Wii version is okay. Miss and Hit
Colors: Even the most cynical critics had to admit that this game was pretty damn good. It took the parts of Unleashed that were well received and improved them, while also cutting out the fat for a much leaner and more satisfying experience. This one ties with SA2 for me. Hit
Generations: Another critical slam dunk; the inclusion of classic Sonic was a major selling point even for people who hadn't liked any of the previous 3D games. I'm not as fond of it as most people seem to be, I rank it just below Adventure. Hit
Lost World: This was a game that nobody asked for. Critics and fans alike were confused and disappointed by it, and I feel pretty much the same. Miss
Forces: Although it didn't exactly get glowing critic reviews, the word of mouth has been fairly positive and I think it's a big step up from Lost World. I'd rank this as a tie with Adventure. Hit
So, altogether that's a ratio of 7:3, or 70% positive. If you include the Genesis trilogy and Mania (4 hits), Shadow the Hedgehog (miss), Secret Rings (hit), and Boom (miss) the ratio is 12:5/71%. If you include the GBA and DS entries (5 hits), it goes up to 17:5/77%. Unless you're grading on a 7-10 scale like most video game critics these days, those are fairly good results.