Not even 3 years ago, if you so much as mentioned Sonic anywhere, be it the internet or real life, you'd be slogged with remarks such as "omfg sonuc cycle!!1!" and "sonix dead y do u play ;//". However, ever since Colors was released, I feel like SEGA have been doing nothing but improving the face of the franchise and bringing it to a reputable status once again. While the games aren't getting scores as high as the latest Mario platformer and the sales aren't quite up there with Uncharted, I feel that the series is finally picking itself up, not even necessarily only as far as overall quality goes, but the face of the franchise as well. Colors got 8s and 9s almost exclusively, with high sales and many seemed to have really enjoyed it. Generations was hyped by Sonic fans old and new, bringing back jaded fans who haven't played a game in years, and making once weary fans eager and excited to play a Sonic game again after countless disappointments.
Now, with Sonic CD hitting the top of the sales charts on Apple's app store and many seeming to love it, I think it's very safe to say that, well, the Sonic series is definitely out of the slump it put itself circa 2004. There really seems to be something to enjoy for all fans, old or new, and the overall quality of the franchise has increased dramatically. People are finally clamoring for the next game, and if they aren't super into modern gameplay, there are 2D games out there for them to enjoy as well. Looking at Sonic 4 critically, I honestly didn't think it was all that special. However, it's released marked the first time a Sonic game was praised in a while, and it of all games was among the first to bring old fans back to the series.
Regardless of your personal views of the franchise, I think it's safe to say that SEGA are on the right track to making Sonic a popular and fun franchise that the whole family can enjoy.