XCOM: Enemy Within

I don't have it but looks like it has bad side effects

I'd suggest watching this video. It's kind of long though.

It adds a ton of maps, mecs, genetic modifications, and a whole new enemy.
If you like Unknown and could see yourself playing multiple times then Within is worth it.

It's quite a new game actually. You like EU? You'll love EW.

Bought it on GMG (with 60% off or so) and have just started on it. Looks like the same but with the addition of generic manipulation. That might make the game pretty interesting to play I think...

If you're going to get it, go to Amazon. Over there it's currently at the lowest price level ever, only $10.

Thanks guys, it's looking good. I am checking reviews right now, and it seems good.

A list of what it has to offer:

• More maps, also designed to add more variety as well as a few callbacks to the original XCom

• 2 new aliens to adopt to - Seekers, which are stealthy and nasty and Mechtoids, Sectoids in battlesuits - giving the little guys a heavy unit that keeps them relevant throughout the campaign

• A faction of human enemies, with soldiers that mimic yours and who like to raise panic levels. These come with their own mission types involving covert operations to hunt them down. Also gives more to do at world map level.

• More research options/foundry projects, including ways to deal with new threats, buffs to SHIVs and more grenade types to give more tactical options etc.

• Rebalancing and reshuffling of soldier skills.

• An optional mini-story similar to Slingshot DLC, with the reward of guaranteed gifted soldiers

• A few more interesting scripted missions which I don't want to spoil here - suffice to say, they're much better done than the Council missions in the base game

• New resource that must be gathered during Abduction and UFO crash/landing site missions, which typically requires more aggressive tactics

• Stuff unlocked ny/paid for with the new resource - build your own battlesuits and turn your soldiers into pilots for them, and genetically reengineer your troops with new abilities (Jump like a Thin Man, buff the squad like a Muton's Blood Call etc.)

• Medals, which give stat boosts to soldiers that you give them to.

• Solid balancing to make it all work, while at the same time making resource management more involved. (I doubt that you'll get everything you want when you want it on higher difficulty levels)

• For the multiplayer: The big change here is that you can finally save your favorite squad layouts instead of having to redesign the squad every time. And it of course also benefits from just having more maps.

U must buy it. is so cool! first game a play in 2014!! :D

I'm currently playing it through for the second time, I love it. It adds to almost every aspect of EU in a positive way. I have two problems with it though:
1) It does have bugs (EU played fine for me, but EW has crashed on me a few times).
2) MINOR SPOILER ALERT, I really didnt like this blatent in-game reference to another game.