Thing is though, with a milestone like the 25th anniversary, SEGA would be idiots to ignore it. And honestly, its not like the franchise is in the gutter. Sonic Boom was mediocre to terrible for sure, with the only bright spots being the comic books and the TV show (which can be hit or miss). But when it comes to the actual Sonic Team output, it hasn't been bad. Since 2011 we've had Generations, Lost World, Transformed and the Olympic Games. Of those we've had some very well received titles (Generations, Transformed), decent titles (Lost World) and the Olympic Games which improved since past releases and have been selling well thanks to the license and Mario's inclusion. On the licensing side of things, we've had some great First 4 Figures statues, Jazwares last hurrah with the brand in the form of the Generations line of toys, quirky stuff like Sonic Monopoly and the Archie Sonic comics underwent a reboot which did away with a lot of the past crap and embraced the games which lead to some great arcs (Genesis, Sonic the Fighters, Sonic/Mega Man crossovers).
So with that all in mind, I really can't label the series as being in a bad state nor can I label the games output as being mediocre to terrible. If people are still festering over the stuff in 2006... they need to get over it. It has been 10 years since then and there is a lot more to celebrate than to be down about when it comes to 25 years of Sonic.
Again, the problem is people thinking that Sonic needs to take the blame for America/Europe not embracing other franchises, though the last 6 months have seen a shift with stuff like Miku, Yakuza, and Valkyria Chronicles getting the spotlight in the West.