Battle: Los Angeles is a good actioner.
It could have been really great had the aliens been a little more tangible, a little more fearsome.

There are many scenes of chaos and urban combat that are done really well. As a former soldier I can say that the military aspects are spot-on, from the dialogue to the equipment to aircraft, bases, weapons, and the way the troops are deployed and organized. Big thumbs up for the military realism. I would've scoffed at this film if it wasn't.
However some main actors seem to remove their brain buckets a lot (helmets) during really intense combat. You never remove your helmet in combat unless you've been injured. Also some decisions that these troops make during the heat of battle would never happen in real life, such as trying to find organs on an alien so they can kill it (with a Rambo knife to boot?).

Aaron Eckhart is a great actor. I think he needs more leading roles in juicy movies. He's the best thing about this movie.
Totally believable as a Marine Staff Sergeant, totally spot-on as an Infantry leader.
The editing is really good. So good you often don't notice it. The editor did a great job. Combat scenes should be edited like this.
The camerawork is in the hand-held style but it doesn't annoy.
Usually hand-held camerawork can irritate the shit out of me, but this style is perfect for the kind of movie this is.

My only complaint is the aliens themselves. We get all kinds of footage of the troops, but only fleeting scant quick cuts of the aliens in action.
It started to resemble a video game after a while during the freeway scene with the bus and all of the close-quarter combat in houses, apartments and on the freeway. I was wishing for the ante to be upped, waiting for some justification for not showing us the aliens any closer than they did. The DVD sleeve says it's "Independence Day meets District 9, only cooler" and that is a good description.
The special effects are well done, and the movie on the whole is well made.

It's just those aliens, man.
They move like George Lucas' Battle Droids, and appear to have some very sophisticated weaponry and flying ships (I liked one of the ships scorching a burned out car with it's massive exhaust vents- good CGI!).

Apparently these aliens are "colonizing" Los Angeles and other parts of the world for the water. The movie begins with meteor showers that ARE NOT meteor showers at all, and the U.S. Marines are called into battle. Character development is minor, but it's there. I didn't really expect much character development anyway from a movie like this.

Bottom line: this is a good way to kill 116 minutes.
It's not Shakespeare, but it's also not Battlefield Earth.
It's a better than average action movie because it moves at a quick pace and it holds one's attention fairly well.
And it has nice sounding battles- if you like loud explosions and the sound of casings hitting the pavement, this is your movie!