So I'm a huge fan of Tower Defense games and have sunk countless hours here on ArmorGames into all three Gemcraft titles as well as Kingdom Rush. I just found out that one of my favorite indie developers (SRRN Games) is running a Kickstarter to fund development of a Tower Defense game, Always Outnumbered, that really pushes the genre to a new place. For those of you into old school RPGs, these are the guys who put out Ash and Ash II, two fantastic iOS titles.
Going by their previous titles, they're great at single player story, but it looks like they are also trying to be the first to design a TD game that can be played direct Player v. Player in a way that isn't simply time trials or high score comparisons. I think it looks fantastic, and I'm excited about a lot of the other non-standard tower mechanics they are incorporating (the KS page explains it better than I can). So I encourage any fans of the genre to check it out and support it if you like what you see!
The Kickstarter is here: http://www.kickstarter.com/projects/2095619008/always-outnumbered