Best yet!
It's amazing to see how every one of these games gets better as it goes along. This one boasts of the best graphics in the entire series. Everything just seems so animated in this. Even the white arrow pointing you to the helicopter seems so three-dimensional and like a character in itself. It was also great to have some backup because it even makes more sense with more people shooting. I love how the enemies in this one just really plop over and fall on their backs.
They seem to be easier to kill and it has a lot more of a story so it's more comprehensible. You really took every flaw there was about this series and corrected it! Considering the first parts were already great, that's very impressive! You can never go wrong by combining defense games and shooters. Zombie stuff forever, my man!