I really enjoy the Gemcraft series, partly owing to the gem combining, but mostly to the fact they're the only defense games I'm good at besides Dungeon Defender. With other TD games I lose interest and patience quickly for whatever reason.
Amazing graphics, which means more eye candy. Rarely do you see TD games move beyound the realm of dull guns and bombs.
A refined concept of TDs, matching colors instead of building different types of guns. The ability to combine ''towers'' or gems, to create even better towers is rather new. The game is much more flexible than the traditional TD since you can move your gems around strategically, whilst utilising other methods to win, such as gem bombing, which is my favourite.
Instead of building static towers, you create a cache of gems which you play around with, which again goes back to the flexibility reason.
Rather than stick to the cliche method of building guns, stationary based towers, or medieval crossbows, the game revolves around using gems, which is a unique concept and makes it a fresh concept, giving the TD genre new life.
And I'm only describing the original game, I've yet to play the sequels which have far better improvements I hear.
The original Gemcraft: http://armorgames.com/play/1716/gemcraft
The sequel: http://armorgames.com/play/3527/gemcraft-chapter-0
The newest: http://armorgames.com/play/10317/gemcraft-labyrinth
I personally like the game for the same reasons previously stated. Just because of the creativity and strategy of mixing gems and the different ways of winning like the gem bomb. It's different than other tower defense games.
