I’ll give it a 6 out of 10. I’m not a big descriptive writer but here goes – I know others here are good reviewers and may chime in.
The first 1/4 - 1/3 were entertaining and clever; AND the last five minutes - turns out the movie is a prequel – nuff said 
But the main antagonist is so over the top it’s not funny. Also the portrayal of British society is quite ugly and mean, not funny except a few spots. It won’t be a hit in Britain. There is the apparent killing of an abominable snowman and NOT in a traditional cartoon-funny technique when it could has been. There are a few spots of adult humor.
Being a car guy, the highlight for me was the amazingly accurate caricatures of real vehicles that kept me looking for detail. The most featured car is an obscure station wagon from 60 years ago – who can identify it? Through the last half of the movie I was mostly watching background graphics for any Easter eggs or adult humor. Didn’t find much.
Definitely for the 10 and under set.