Clunky controls and unrewarding combat make playing the game feel like a chore to simply progress through the story line
Great story line and atmosphere immediately immerses you in a 1960's world being invaded by aliens. You are connected to the hopelessness of fighting a far superior enemy, and unless you set it to "easy," you'll find yourself dead quite often, always being outmanned and outgunned.
The bad -
None of the early guns are fun to play - at all. You often have to unload a full clip, or more, into an enemy to kill them. You soon realize the only weapon worth using is the sniper rifle, which quickly elevates you from one-clip one-kill to one-shot one-kill. It's not really a winning FPS formula.
The combat is often punishing, and it's not uncommon to take a sticky grenade to the face and find yourself fleeing like a panicked halo-AI who was just stuck, reserving no dignity for your impending death. When sprinting to cover, your character doesn't always TAKE cover. Sometimes he stands there and you have to mash space+shift until he figures out what he needs to do. Other times you'll be sprinting to flank and your champ decides to stick to a wall he passes on the way.
As well-intentioned as the tactics are, any attempt to flank the enemy often results in that squad-mate being ambushed because they're now solo, leaving you to sprint the map to save them. When I wasn't sniping and felt the need to flank the enemy personally, I found myself simply using my squad-mates as decoys only to have them get up and move because I ran too far and left some invisible maximum range, leaving them exposed. Flanking yourself often means running laps to revive dead "decoys".
Going on missions generally gives you a new gun or a new backpack or something, but overall feels unrewarding. You can't do anything with the bounty and scrap resulting from the mission. I found myself just trying to get through the missions to see where the story was going.
There's no strategy here, either. Only FPS and some tactics. There are no tech trees, no base building, finance management, etc. Your troops will level up, but there's nothing that -really- separates two supports from each other. Being a linear story line, there's really no replay value here, either. There's nothing that's going to change one play-through from another.
I'm tired of seeing great titles being dumbed down to reach wider audiences, only to fail miserably. It's generally not a great scientific feat to understand what has attributed to the success of many great games, and it's a bad idea to simplify a great formula because it makes the game feel shallow.
A great strategy game is one that gives you a broad range of tactical depth and choices, but does so in a way that's approachable and rewarding. A great FPS game gives you great control with your character, and a great selection of guns that get progressively better during the game. XCOM achieves neither of these well, and is a poor attempt to convert a strategy game to a shooter, retaining very little of what makes either genre FUN.
I hope the developers and publishers take this as a lesson learned: XCOM is a brand recognized for its great strategy and tactical depth. If you want to try something really great and innovative, why corrupt your brand? People are paying to be entertained. Why not just give them what they want?
When someone walks into a room and suggests turning Sid Meier's Civilization into an FPS, they should be immediately pelted with rotten fruit. The same should have happened when the person who suggested turning XCOM into a shooter.
Give me more of XCOM: Enemy Unknown - just make it better. I have money. I want you to take it, but only if you give me what >I< want. Why is that so hard to understand?