A couple of bugs: about every time I pressed "start wave" on the "wave" tab, I entered the wave with my drone in "battle" mode, which I did not want. At least once, I started in "medic" mode inadvertently as well, but I'm not sure about the context. That was a confusing moment; I thought the new kind of bugs were healed by my drone bullets, it turned out everything was healed by my drone bullets.
I can tell what everything is supposed to be by looking at it. Presentation star get!
The mechanics are sort of a neat little mashup of defense, tactical, shooter, and RPG, each in its own micro sort of way. The mix works and produces fun. Not afraid to kill you right away, which means your target gamer is not a crybaby. Thanks for the respect.
I think what most critics are referring to as difficulty is more accurately described as "trial and error gameplay". When I lose, whether it's a barricade, a veteran sniper, or the whole base, it's usually because I did something wrong. There is something I could have done to prevent it. But there was no indication (with some big exceptions) what I should have done before it happened. That doesn't mean the game is hard, it just means the game is hard the first time you try to do anything.
I don't think the manual is quite enough to "reduce casualties" as you put it. It's enough to explain the interface, which is absolutely necessary; even with a lot of stuff locked at first, it looks a little intellectually intimidating. The manual tells you how to play, but really doesn't say anything about how to win. You still need trial and error to figure out how a lot of key things work.
The differences between unit types and what makes them effective or not effective, in particular, I did not see as being intuitive or adequately conveyed by the documentation and interface. I expected, for example, the gunner to be great at suppression fire, but it turned out to be terrible at suppression fire, which I discovered by losing a barricade, the gunner, and another unit. The plain old marine is the best at suppression fire because his bullets kick most enemies back all the way to the edge of his range, whereas gunner bullets do not seem to bother martians until they suddenly die. The same could be said of the railgun, but they do tend to suddenly die on the first shot.
The manual also fails to portend the underground worms that can fry your units that are behind perfectly healthy barricades. That I learned by having 5 experienced units fried from behind nice strong barricades. It doesn't say that your units can fire from behind barricades either, but you can figure that out from the interface without taking any losses.
I'm still figuring out the enemy color coding, of which the manual makes no mention. The black things take little damage from your units but are weak to drone fire, correct? It sure seems that way, and if I made a habit of using the drone in medic mode, I'm pretty sure I could have lost on the first wave where I encountered them. The mystery is the green bugs; how the hell do I kill the green bugs? I know something works because one or two of them did die, but if it doesn't have some critical weakness like the black giants, then it just has an unreasonable amount of HP.
All things considered, good game, I like it. Doesn't treat me like I'm going to run and cry when I lose, which you would think is what happens in most modern games that have an auto-save every time you successfully blink.