Excubitor's blending of tower defense and space-based shooter means that it has to figure out the best way to handle both genres' expected control schemes, and it is in how the developers attempted to tackle this problem where
Excubitor can have a lot of issues.
Excubitor uses the mouse to not only select which turrets you want to install, sell or upgrade, but it is also your target reticle. On the surface, this doesn't feel too bad. It turns the shooting almost into a point-and-click control scheme except that you aren't selecting enemies and locking in on them, you are simply pointing at the spot you want your weapons to hit, and if there happens to be enemies there, so much the better.
The problem is, the mouse input itself can be really rough. When I first played the game, I had a basic, no-bells or whistles, optical mouse hooked up. The result was a complete lack of control in my cursor's position and an impossible gameplay experience. What I eventually found was that I needed to use a mouse that had a bit more customizability built into it. What you are looking for is something that has an adjustable dpi so that you can tune the mouse to the input the game is expecting, because if you don't, you will have a hard time even navigating around the tutorial level.
I have to say, this early experience really soured my first impressions of this game, and it wasn't until I found the right mouse for the job that I was able to make real progress and see what Excubitor really had to offer.
Excubitor is a game with a fairly unforgiving learning curve. The basics aren't difficult to understand, but from the start, you will find yourself knee-deep in tough missions. The ability to upgrade your ship and unlock a lot of different weapons and turrets as the game progresses means that you will end up with enough options to find a loadout that fits your needs, but the game can be both intense and even exhausting.