I didn't think it was horrible, but it's nothing special. They definitely should have just gotten rid of the alien "reveal" shots towards the end. That was some really really bad CGI, which really put a whole damper/SyFy budget movie on the visuals since up to that point, it was pretty decent for a low-budget film (the orange electric, the shots of people turning to ash, etc).
Of course, you can nitpick it to death: I think they spent way too much time trying to build up characters, which very little payoff. For example, these guys are supposed to be tech geniuses, yet I waited the entire movie for them to come up with some sortof plan, which they never did. Same with the guy they run into that has built himself an entire cage and microwave gun? How did he know to do all of that and how did he have time? Why did the girl run 1/2 mile inland to hide in a bus instead of swimming 50 feet to the sub?
Regardless, while the film could use a lot of work with some parts re-written, it was worth a rental and I was mostly entertained.