In a sense, it is silly for me to post a review for this game since this is such a love-it-or-hate-it game that there is no way to tell if you like it except by playing it yourself. (Quite conveniently there is a demo.)
I will admit, I was afraid that this game would be next in a streak of bad purchases on my part. E.Y.E quickly showed me that my doubts were unfounded.
E.Y.E is a combat focused fps/rpg, and the combat is amazing. In this game, an assault rifle is not a bullet hose; it is a deadly weapon with high recoil and each shot having extreme stopping power. The hunting rifle feels like it could kill a god. The Damocles sword causes explosions on hit and can block bullets.
In addition to all that, your play style can be augmented with powers such as the cloak (A la Crysis) or the dermal sheath to enhance your armor. You can obtain spells that can drive a target insane to stir up chaos within a horde or you can implode an enemy and teleport to where it used to be.
Most of this is unlocked by spending money (Brouzouf) at the temple HQ. In addition to that, you spend money to purchase cybernetic upgrades anywhere which enhance your powers and statistics.
In addition to all that, you can save multiple characters that play wildly differently.
Now for the bad stuff. This game is prone to bugs, including an unfortunate bug that causes saving to not work sometimes. That is the number one word of caution I'd issue to potential customers, but if you are willing to put up with it you will be rewarded.
As others have said, this game does not explain itself very well. I didn't have too much trouble getting into it, but some will. (I would suggest using auto skill point allocation on your first attempt.) A more diplomatic reviewer would say that there is a strong element of discovery; the fact that this game tells you so little means you can play for months and still find something completely new.
And there are bizarre and often unnecessary mechanics such as sanity, which can be nullified by the research system. Dying has potential to leave a permanent statistical penalty, except that it's not really permanent. You can also get rid of that with the research system. (The research system being one of the most bizarre and unintuitive parts of the game.)
Having said all of that, I would still strongly recomend this title to anybody that has patience for a game that is a little rough around the edges. Very few games are as rewarding as this, and for $10 it is an excelent value.