Its a tower defense game with the tried and true formula of you defending your base against incoming creeps with your towers. However, this game differentiates itself from other Tower Defense game in 2 regards. First of all, just building towers wont get you anywhere. The game is HARD. Your towers have energy levels that affect the performance of these towers and you will need to adjust these energy levels accordingly to allow for the best possible level progress. It has some undeniable puzzle elements in that regard. The level design is also rather refreshing since it sometimes cleverly uses genre tropes against the player. E.g. Most powerful tower is always the best one to use? Wrong.
Another distinctive element and the reason I enjoy this game as much as I do, is the interactive electronic/house-y soundtrack. The music changes depending on where you place your towers and which energy levels you provide them with. The effects are sometimes rather subtle, in other times make a striking track to an outstanding one. Oh and yeah, the soundtrack is just way too good to be not exposed to a bigger audience. Its a game I mainly play for the soundtrack, to delve 20-30 minutes into these tracks and play a game that has been made with that soundtrack in mind. Its that good. Unfortunately, the track in the youtube video on the devs website isnt really the strongest selling point in that regard, but I highly recommend checking out the browser 2 level demo (The full version is downloadable). Completion might take you an estimated 20-30 hours if you are a somewhat decent player.