I've been following this game for some time, and there are some nice original concepts in this one which I have never heard of in a tower defense genre.
The graphics in this game is pretty nice, I like the environments and every level is different. The environment is not just for the sight seeing, it plays a role in your strategy and the paths taken by the AI is modified by it. You will need to adapt quickly and devise an optimal route in which you want attackers to take.
In the game, you will be creating a path for the AI to take, but unlike most tower defense games, you can block the path. However, AI will start to attack if there is no other way, and you will lose towers or crystals as the game calls them - which could be part of your strategy.
While planning your maze, be advised that it is not always the best plan to put your core to the furthest possible corner. Your crystals will need power and the source is your core. You might start dropping random crystals around, but those would be ineffective compared to the powered ones. Also note that only the same type of crystals can carry or transmit the power between each other, i.e. if you want to place some powered red crystal towards the gate, you will need to create a path of such crystals starting from your core.
Luckily you can stack crystals on top of each other, so it is not a 2D maze you are trying to construct but a 3D one. If you place a crystal on top of another one, it will drop and replace if the bottommost one is destroyed. This gives you some buffer before attackers can breach if you are busy somewhere else. If you want you can also construct crystals above the ground, but they should be touching to an existing crystal on the same level.
There are 5-6 different types of crystals, each with different abilities, as most tower defense games you have some attacker crystals, some slowing down crystals, some AOE crytals. The interesting ones I could call a "tank" crystal, which has high health but has no attack, so that it can guard other crystals behind it. There is also a teleporter crystal, which can charge and teleport attackers further away. One other type of crystal is used to gain more resources, if you can find a ray of light in the level, and place those there they can generate resources for you.
While working with all these, you will struggle to look around for hidden chests, that might appear from time to time. Those will give you some extra resources which you will definitely need. I remember a point in game trying to find a chest where I had no remaining resources and an orc was trying to destroy my last green crystal before the core.
This game will not hand you the success in a golden platter, you will need to work hard for a strategy and the weakest point in your defense will fail you, easily. And I'm talking about the "normal" difficulty mode, the game also has "hard" and "hell" modes for the hardcore gamers.
I agree that I had to spend some time to get used to the controls, however you won't have any problems once you are familiar with the game. And actually they are not that complicated, you can play the whole game with just mouse if you want.
I believe the game has high replay value, as placing core to a different position can change your game experience altogether, or changing your strategy in terms of maze planning will change everything. Considering the different difficulty settings, if you need to spend more time, you will find a level for your needs.
In my opinion game has a nice price point, considering the amount of time one can spend on this. I believe Tiestru brings a nice touch to all those tower defense fans.