It's fine, but predictable. The baddie isn't truly bad, deep down, and only needs to be persuaded that he was wrong and reunited with his children, etc. The film's okay and is indeed one of the most profitable of the franchise's films to date, but it's the kind of thing that you'd sit through peacefully rather than be surprised or excited by. You'd probably only be seeing it because you were taking your offspring or something.
Firstly, some background. Doraemon (started in 1969) is the top-grossing anime franchise of all time and the 11th top-grossing animation franchise worldwide. These films started in 1980 and there's a new one every year, but they're slightly different from the TV series. (Personally, I don't think they're as good.) They'll have a plot. They'll be more action-orientated, being proper adventure films instead of just comedy shorts. Admittedly the franchise can handle this and Tomoko quite likes these films, but I think they're merely okay and have a credibility problem in the fact that Doraemon's gadgets can do absolutely anything. Time travel, magic, flight, whatever. This particular film spoils us rotten with lots of cool gadgets early on to make us go "oooooooooh", then sweeps them under the carpet and expects us to forget about them.
We begin with an all-action pirate fantasy that turns out to be a daydream of Nobita's. He's been reading Robert Louis Stevenson. "Let's look for a treasure island!" he cries. Everyone pours cold realism on his dream... but Doraemon pulls out a 22nd century magic moving map. Nobita touches it, the map glows and suddenly the TV news is announcing that a new island has appeared from the sea in exactly the spot Nobita indicated.
"Let's go!" says Doraemon.
"No," says Nobita. Eh? "It needs to be more pirate-y."
Doraemon duly produces a build-it-yourself replica pirate boat kit, a "magic growth" beam to make it life-size and a captain's hat which makes everything look more 18th century when you wear it. This is pretty nifty, so off everyone goes for nautical adventures!
The first pirates they meet are planning to send them to the bottom of the sea! (You'll forget later that there had been any hint of murderous intent, but I think this might actually be a play on the fact that the pirates have an underwater base.) They capture Shizuka because they think she's someone called Sarah, which in a Japanese accent sounds like "sailor". This splits the film along gender lines for a while, with Shizuka and Sarah having a long chat and meeting some of the memorable women who help run things on the ship. Meanwhile the other four members of the Doraemon Gang meet Sarah's brother and get in more danger.
There's family stuff! The baddie is Sarah's dad, having turned all upset and misguided five years ago when his wife died. She was the scientist who built their ship. They're space-time pirates! One of the film's nicer touches is a robot parrot that still imitates some of the mother's mannerisms. Now, though, the priority is to stop Dad from draining all the Earth's energy so that he can spacewarp to another planet instead. (Wouldn't time travel use more energy than space travel? Well, never mind.) That's his idea of keeping a promise he made her. Tch, dad. And you thought your parents were embarrassing.
This film is a pretty good example of what it is. It's efficient, exciting-ish and perfectly watchable, assuming you're not expecting too much. You'd recommend it to a small child, although not quite so strongly to a parent who's seen a few of these before. It's got nice animation. Nobita's Doraemon-saving dive at the finale is awesome. The film's doing its job.