When I play games like Civilization, I lose time. I look up at the clock after a play session and more time has passed than I expected. When I play XCOM, I gain time. The clock shows that less time has passed than expected. I suspect this is a result of the tension that XCOM creates during play.
XCOM is my current game that I recommend to my gamer friends. It is an tight, focused experience that creates a deeply personal feeling of victory and defeat no matter which difficulty level you play on.
Due to the steam sale and recommendations from friends, I also picked up both Endless Space and Sword of the Stars II, two space-based 4x games. I've not really had the time to dive into them in a serious manner, but have managed to clock the first hour or so in each title. My first impression of Endless Space is one similar to a civilization game: a new player feels pretty comfortable diving in and just doing stuff. Sword of the Stars II, however, feels much more like a traditional Paradox game: dense, meaty, and requiring a lot of reading and flailing about.