Immortal Defense
There are 26 types of enemies, each with its own abilities and unique interactions with one another, and 11 types of towers, each of which goes through different forms as they are upgraded, and each of which gains new abilities as the player collects achievements. There is a way to turn the visual options down, but even with all the options turned down, it can still be quite flashy.Immortal Defense has a story-driven campaign with 100 core levels and 50 optional side-quest levels (which can be completed for bonuses that help you with the core levels).Note: The game was first released on May 31, 2007, and was updated with new content in 2009, and then again significantly improved for its Steam release in August 2015.