Okay, non spoilery first... nothing here you won't be know if you've seen the trailers...
The premise is pretty basic; it starts with a flashback in which we have discover an Earth-like planet in a nearby star system and transmit a message towards it. Cut to the present and the aliens arrive looking for trouble. They dome off an area of the sea behind a force field, but some ships are trapped inside and they duke it out.
The special effects are very spectacular. You can generally see what's going on - not very much in the way of hideous camera shake, thankfully. There's plenty of views of missiles being launched, and CIWS firing, and cannon firing, and alien weapons firing, and stuff blowing up.
Beyond that... well the characters are paper thing. The designated hero is a guy with the potential to be the best of the best, but his immaturity lets him down. Naturally this translates into him being able to win, if only he can become all he can be - the big question is whether he will be able to learn the lessons of maturity and apply them to dealing with the aliens. I won't spoil it, of course, but take a wild guess and you probably won't be wrong.
The game origin is rather more clear here than in some similar films. They come up with a way to scan for the aliens and decide to depict it as a grid, complete with letters and numbers. So they literally do say "C-7!" - missiles fire - "Miss!" It's rather silly, but it lasts about five minutes and then they stop focusing on that and move on.
Outside him there's two ladies - Rihanna is Raikes, whose entire role sums up to saying "You be careful now!" and pulling the trigger on the weapons once the hero achieves the shot. She's pretty, she speaks her lines quite naturally, and generally does a servicable job. She gets no chance to act as such, but you certainly wouldn't know it was her first acting gig. I expect we will see more.
The other woman is Brooklyn Decker as Samantha. Her job is basically to have a large chest in tight outfits and be the hero's reward. Since they wanted to give her something to do, she accompanies a soldier on land and helps him out a bit on his efforts to fight the aliens. He doesn't have a chest like hers, but he's actually a much more interesting character. Without going too far into spoilerland, he's a wounded veteran soldier who lost his legs and walks around on artificial limbs. He's caught up in the action and forced to do his best. I think it's fascinating that a film like this would actually dwell on the human cost of warfare; normally action movies like to show people either being alive or dead, or possibly having "manly" wounds - grazes, cuts, but nothing really fundamental.
All in all, this is exactly what you would expect. Big budget, loud, nice to look at, and rather stupid and preposterous. Watch it, if you're into that sort of thing.
Now, more detail, complaints, and spoilers!
Then there's the aliens. They have no real motivation. They want to invade Earth and occupy it, yet the film makes a point of the fact that our daylight is far too bright for them to handle. So... why are they here then? They don't appear to be nocturnal or anything... it seems an odd choice to invade a planet that's not terribly well suited to your physiology. And of course, the aliens are badass powerful, but turn out to have flaws which make them relatively easily defeated in the end. Much like in Battle LA, Independence Day, etc. Yawn.
Now I know technical accuracy isn't a big deal to a film like this, but... I had figured, seeing the trailers, that the premise was that the Navy had put the Iowas back into commission. Or that the film would be set 20 or so years ago. Or something! But no... it's present day and the ship is retired. But you see, only three destroyers are within the force field, and they all get sunk. So what remains of our heroes decide to put the Missouri back into commission. There's like 20 of these guys, and they don't know how to run the old ship... but the veterans who attended a ceremony on the ship at the start are still around, so they man the ship. There's about 20 of them, that we see, as well. And these guys put a museum piece battleship back into commission as a functioning warship, in the space of about two hours. They literally just cut the chains, start the engines, and sail off. Working shells are still aboard... live powder bags are still aboard... there's fuel on board... Then they attack the alien ship by sailing right up next to it. They're literally within about 500 yards when they open fire. It's laughable, so if stuff like that bothers you, beware!
Anyway, I could go on about the flaws but that's enough of that! Overall, I'd rate it about 5/10.