This is one of the best, if not the best, pure tower defense games in a very long time. Depth: There are numerous enemies with lots of different abilities, defenses, speed, etc. 20 towers, each customizable by placing points into them. Most of them have 3 upgrades in game, a few only have 2. I counted 47 levels, but the map is kinda a mess so I could have easily missed one or two. Challenge: You can adapt any of the levels to be as easy or difficult as you'd like. Need to just beat a level to get the rewards (new tower or gems) but having problems? Tone it down a bit with the "Breeze" rune. Looking for a challenge? Load up to 10 different runes increasinng the difficulty greatly, but also the reward! Looking to go nuts? Turn on the "Endless" rune and get ready for an increasingly difficult grind. Replayabilty: With all of the customization available, you can replay this game until your mouse breaks, buy a new mouse, then keep playing some more. There is no end to the fun. I highly recommend this game.