Finally got my hands on this, and as someone who has been a huge fan of the original Xcom series (I've played the first three games) I have a couple comments to make on this game (I'll also be address previous posters, but not by name).
The first is story. I'm enjoying the story at the base. Its so far a more detailed storyline then the original games. The originals did have a plot that moved forward. At one point the alien threat becomes to overwhelming for the player that it has to be progressed. This game provides a little more in between the major events that the first games plots were built around.
The next is the tactical combat. I get it. Its a nice modern system that works well to get the more action gamers involved. I like it too, but after playing a lot of Xcom: UFO Defense I do miss the old system. Especially the monster closet thing. I've yet to be fired upon from the fog of war (which happens a lot in classic Xcom since the aliens have better eyes then the human operatives) which takes some of the tension away. Plus hearing the doors open during the aliens turns always created tension for me.
The ant farm is a little frustrating. The reason is everything needs resources, and I'm used to the first game where you can produce alien alloys. I'm pretty much out, and the only time you get them is shooting down UFOs (and I only encounter one a month in the game).
Overall a great game. I love turn based tactical games, and this one is well done. I'm playing the PS3 version, although I bet this game is awesome on the PC.