I'm not overly picky when it comes to special effects, for years I was haunted by the idea of birds attacking after seeing Alfred Hitchcock's The Birds. Those effects weren't even all that great and they got to me, so you kind of get the idea that it doesn't take much for me. That being said I thought the special effects in this movie were pretty good. I found the aliens that were hunting for number four were really creepy looking. Each time someone from either set of alien beings was killed they simply turned into dust and floated away, which made it very easy to hide what had happened. At one point there is a fight at the high school and the destruction was huge, but no bodies were left. That one was going to be a little more difficult to explain by the authorities, although with the other weird things that had been happening that night it might not have been quite as big an issue.
The actors each did a good job in their roles, I was able to buy them all as the character they were playing. It helped that most of them were not too well known already. Yes the lead is also in Beastly and the one female character is from Glee (which I do not watch so that didn't make any difference to me at all), but no one jumped out at me as someone I associated with just one role which can be distracting. The one I knew most well was Timothy Olyphant and even him I haven't seen in too many roles. Lately I haven't been watching a lot of movies or TV so this was a nice break.