The only thing more terrifying than the aliens are the bugs that invaded this otherwise superb game.
I love the unknown. What lies beneath that murky fog of war? What kinds of upgrades are going to be available for my Assault trooper when she gets promoted to Major? What will Dr. Vahlen find when she performs an autopsy on that brutish Muton corpse I delivered to her? Oh dear God, what is that? XCOM: Enemy Unknown delivers on it's promise of the unknown, of treading a path that mankind has (thankfully) never been down before. It is built on a concept and a premise that is bound to deliver, but this Mercedes gameplay is put together using Kia parts.
Graphically XCOM is a treat, the character design is consistently enjoyable; from the Agent Smith inspired Thin Men to the classic Grey inspired Sectoids to the mysteriously malicious Ethereals, the enemy designs are classic UFO, alien fare. You won't be blown away by the graphics engine putting it all out there, but in this kind of game, you really shouldn't be expecting that anyway. All of the sound effects are top-notch as well, from alien bodies splattering to the sound of a souped up shotgun launching an alien corpse through the air.
The clock read 9:45 PM. I knew that at 10:00 PM I was going to turn off XCOM so I could go turn on the PC, check the broker to see if any of my auction items had sold, then go to sleep. This cycle continued every 15 minutes until finally, 5 minutes after midnight, I turned it off and went to bed. All of the addictive qualities of Civilization (now that I have that library built, I can finally get back to producing knights and rid the Earth of the dreadful Aztecs) are brilliantly broken up by the randomly random tactical battles. These firefights are brutal and intense, and (while not up to the standards set by Valkyria Chronicles) really demand your focus and attention. The unit types, though seemingly lacking in variety, are just diverse enough to keep it interesting, and each unit fills a very specific and needed role (the possible exception being Heavies).
However, these tactical battles are also where things start to go awry for XCOM. Bugs, glitches, and good old fashioned negligence do their best to spoil an otherwise brilliant effort. My game froze three times during my playthrough, requiring a hard reset each time. Load screens after missions will randomly cause major graphical glitches that persist until you load an earlier save. The volume will drop out, and then 5 minutes later mysteriously pop back in. While these are all annoyances, the gameplay bugs are the more frustrating.
An example of a bug combined with a development oversight: That Muton must needs die. I decide to end its filthy existence with a shot to the face from my high powered Plasma Rifle. From where I stand, he has high-cover, so my chance to hit is only 48%. I select Run and Gun so I can move into position to flank him, removing his cover bonus. I move around to his flank where he is uncovered, thus removing the -40% hit chance, or so I thought. Even though this filthy Muton is standing 12 feet away from me at this point with nothing to get in the way of my plasma blast except for such petty air, the Muton is suddenly untargetable. No matter what I do, the game simply won't let me select him as a target. His Floater buddy that I can't see because he is standing behind a wall 35 feet away is a valid target, but this filthy Muton somehow is not. This could have all been avoided if they would have simply made a dynamic target list that reflected who is targetable while you are in the movement phase decided where to move to. I can't tell you how many times I moved in for the kill with my shotty only to have this target that I could virtually reach out and touch not be a selectable target.
Even without some much needed improvements to the battle interface, if they simply would've cleaned up the bugs that infest the otherwise terrific skirmishes, I would rate XCOM at a 9.1. As is, the end game mission becomes a repetitive sequence of saving after just about every move, because you have no idea if the game will even allow you to shoot the fool that deserves to die standing 15 feet away from you. A wonderful game, marred by dropping the ball on the QA side.