I go to Transformers to see Megan Fox look good and giant robots fight. I went to Battle: LA to see the American military and aliens shoot and blow each other up.
A lot of people seem to think this was supposed to be some kind of District 9 movie. Sure, if you evaluate it on the same scale as District 9, it sucks. But if you just wanted to see an awesome action movie, this is the movie for you.
Yes, there was no character development. Yes, the plot is a zillion years old. So what? I wasn't looking for those things. Now and then, it's nice to go see a movie with mindless action. 100% of this movie was mindless action. Suspend your disbelief and enjoy it. Compare it to a movie like The Losers or A-Team where the movie tries to build up some characters and an original plot and fail miserably.
I would also like to add that there are some nice original points to this movie. For once, the aliens are not infallible. I get pretty tired of the oh-lawd-we-hit-them-with-nukes-and-didn't-kill-one type of alien movie popularized by Independence Day. There is no magic bullet in this movie, the aliens die from bullets, and you have to take out the command and control center to do serious damage (hey, just like in a conventional land war!). I also thought this movie was a decent depiction of a realistic military response to an alien attack. Everyone mobilizes, surrounds the landing zone, and combat ensues when they are attacked. Pretty simple.
I also see complaints about camera style. I honestly didn't even notice. It didn't seem any worse than, say, Black Hawk Down.
So I give this movie 8/10 on my action movie scale. If you were planning on evaluating it on the thoughtful-work-of-art scale, you must not have seen any of the trailers.