Umm... let me see, that's Eggman on top, with a metal Sonic proto-type and a deranged anteater... With Sonic's great-grandfather on the bottom, with Tails' rich uncle, and that lady from the Flintstones...
Seriously though, it doesn't look bad, but just doesn't look like Sonic and co. to me... Knuckles the spiny anteater may be more realistic, but definitely looks more absurd. (if that makes sense)
Sonic's features are too thick and furry, while he is supposed to be sleek and streamlined. Tails looks too grown-up or 'cool'... He's supposed to be cute. Amy also looks too grown up and... she looks... human. Knuckles face looks a little odd with the long nose... Eggman looks okay, but then again... he's the only human in the picture... Metal Sonic looks like something from an old Godzilla movie.
No offense directed, but I'd rather have Sonic and co. be caricatures of their personality than accurate sketches of the animals they are.