I thought it was very good. Largely due to Gadot who I think is perfectly cast, in that she's able to pull off the combination of feeling naive and innocent with looking strong and purposeful that the role demands.
The early scenes in Themyscira were possibly the highlight of the film for me, I enjoyed every minute of that and I loved the actress who played Diana as a child. The action is pretty great throughout (especially the assault on the beach of Paradise Island - shades of '300' there in places) and Jenkins has a great eye for an arresting image. Some really nicely composed shots and some well-choreographed setpieces (in that you can actually tell what's going on in them).
Pine is good as Trevor, he isn't asked to stretch himself but it's a well enough written part that fits into the plot nicely. I appreciated that the romance was played relatively lightly while still being important to the story.
The story itself is fairly by-numbers but it works. A couple of the twists were pretty obvious but still worked nevertheless when their moment came, which is always a good sign. I have to admit though that I was surprised by the reveal of Thewlis as Ares (but then I've been actively avoiding finding out anything else about this movie since the last trailer came out so maybe that's common knowledge at this point).
The spots of humour worked for me even when it was fairly familiar stuff, and the handling of the WWI aspects was solid and never felt like a cheap backdrop for the movie. The feminism stuff was perhaps underplayed a bit, given the era, but probably better that than the other extreme.
The few weaknesses aside (including a couple of slightly dodgy effects shots, an unnecessary framing sequence that seems to exist only to play to the shared-universe aspects, and an action climax between WW and Ares that never feels weighty because their powers have been so ill-defined up to that point) I enjoyed it a lot.
Most of all it's just a pleasant surprise to see such an unashamedly old-fashioned and 'pure' superhero story at a time when a lot of other superhero movies are trying so hard to mark themselves out as different. It shows that there's still a place for a straightforward film like this if done well.