Even though the plot seems basic and plain, the humour and sheer site of Sonic makes the movie a must see. At first I didn't know if I should see the movie but given I was a Sonic fan I saw it anyways because, its Sonic! When I saw it, it had great CGI and a really sweet side story about friendship. I would recommend this movie a lot.
P.S If you watch the movie, stay to half way through the credits! There is an amazing surprise for Sonic fans!