Just got back from watching it with my older brother and I can definitely confirm that it has a healthy amount of fanservice, but was an entertaining movie in general.I've heard if you're a Sonic fan, you'll dig it, which I guess is the most you can ask for.
My older bro was a huge fan during the Genesis/Saturn days, and although he fell off as he got older, he was down to give it a shot after seeing the redesign. I liked the series despite being a Mario die hard during the Ninty/Sega war, but never got a proper crack at it until Adventure 2 when it was ported to the GameCube. Needless to say, I was hooked and became a bonafide fan when I played Advance and Mega Collection.
Overall, it's an 8/10 in my book. Sonic's backstory came and went in the blink of an eye while Neal McDonough was inexcusably wasted, but Carrey's Robotnik, Schwartz's Sonic, and the sheer level of TLC that went into this movie alongside Sonic's redesign really made this a fun ride.