That's a pretty good question and I've never sat down and wrote a list of things I like about it. First time for everything though...

[After writing out this list, I actually think doing something similar for favorite games would be a good way to get more content here]

• In general, I'm drawn toward "engine building" games
• there's something comforting about the game having a defined end after four rounds (rather than when some victory condition is met)... note that this doesn't necessarily mean the game plays quickly!
• the end of round goals (one of the way you can score points) are randomized. This keeps things fresh
• the "bonus goals" (which are another way to score points) are also randomized on a per-player basis, which creates an interesting asymmetry... all players are working to score points, but each player's path to that end is different
• (i think this has a lot to do with the randomized nature of the end of round goals and bonus goals) plays great with just 2 people but also fun with 5-7 (6 and 7 player variants require the Asia expansion)
• it may not seem like it at first but there actually can be quite a bit of player interaction
• the artwork is really gorgeous... will have to take a pic next time we play for an example
• the components are fairly high quality for the price point
• despite the relative complexity/weight, setup and breakdown are really easy

Overall, I very much recommend it. That said, there are things i dont like as much about it

• people are generally intimidated by the complexity the first time they play. I have found though that about 3/4 through the first game things start to click.
• because it has a lot of randomization via card draw and dice roll, there is a fair bit of luck involved. Sometimes you just don't get the cards.
• although there is some player interaction, I wish there was more. I think this is addressed in one of the expansions (but admittedly I haven't played all of the expansions)

The only game I like more is Terraforming Mars. I play it less, though, as it's a but longer and the folks I play with don't like it as much.