Just beat this game. I could say that it took me like 20 hours or so. I started it in Normal difficulty but before finishing the first mission I had to lower the difficulty to the easiest of all and beside that the game still was very challenging. The structure of the game makes it very repetitive, I mean, each mission the same: 3, 4 or 5 ambush-like of bunch of enemies, you have to run like crazy in small environment trying to use technique to keep alive (like pressing "Y" to get armor from the enemy, "B" to move fast around, "X" to use the saw to get ammo, "RS" to smash enemies to get lives), and you have to do this thousand of times.
Each enemy has its weaknesses, and you need to exploit it (again and again and again and again for 20 hours).
Now, the graphics are great, the design good enough, all the game is very well polished.
I think it is a good game but I do not like to waste time trying to do the same thing 1000 times, and dying 100 of times. I mean, not my style (it is like playing Call of Duty in Hardened or Survival, you enjoy it if you choose that, in this case, even in easiest mode, you may suffer without option).
My recommendation: a) Go to the easiest mode, b) level up ammo first, then live, c) when leveling up, try first grenade, the sniper (rifle), then all the rest, d) In the ship you will find the places to put the battery, try to place them first to get Crystal to increase ammo capacity and live capacity, and e) try to master from the beginning the techniques to get live, shield and ammo, even if you do not needed, just for practicing purposes. That will make the game easier the the long run. Enjoy it.