Before we really get into this, I need to make one thing clear. XCOM is a series very near and dear to me. I cut my gaming teeth on UFO Defense and Terror from the Deep and I've been waiting for another proper XCOM game for about 15 years.
Firaxis has managed to take the original 1994 game and tweak it and polish it into a game accessible to any level of player. Where UFO Defense was brutally difficult, even on it's easiest setting, Enemy Unknown has properly scaled the difficulty to the appropriate levels. Easy is still a challenge, but it's unlikely you'll see the kind of losses we veterans are used to. If you're new to the series and want a taste of what the older games were like, go ahead and start a game on "classic" mode. Just don't get too attached to your squads.
When 2k games first announced that they had acquired the XCOM licence I was skeptical, if not optimistic. The FPS XCOM has been mired in delays and lack of detail and exposure and may not even actually exist at this point. Whatever the case for the other title, Enemy Unknown is everything I could have ever asked for in an XCOM game.
Firaxis has distilled everything that made the originals great and added in their own personality to the title. Gone are the long hours spent shooting down UFO after UFO without any idea of what it was that would advance the plot. Now you always have a goal displayed for you, though when you choose to complete that goal is up to you.
Your squads are also improved greatly. Each member of your squad starts as a rookie, and as soon as they are promoted, they are given a class that will define their role in all the missions moving forward. This helps streamline the gameplay and keep each mission from getting too confusing.
There really isn't enough time for me to go over everything that XCOM gets right in this preview. All I can really say is that you owe it to yourself to at least play it once. It's not just a great strategy game, it's easily the best game I've played this year, if not these past 15 years.
PS: Stay tuned for a larger review of Enemy Unknown.