Pretty fun. Up to mission 17 or something around there.
The repetitive all creatures of one type city missions are boring (i.e. ants in city, move to next area, ants, move, ants).
But I've started to see some variety like some beach missions (those are awesome), the hectors which are huge, cool, make massive explosions, etc. The big circle UFO that drops that 4 legger. Etc. And actually the ant fest in the underground caves was a nice change of pace too.
Nice variety of weapons. As long as I keep seeing more environment variety I'm digging it.