Like Civilization? Want to play the longest Civilization game of your life in the form of a browser-based MMO? Sounds like Travian is for you. Travian is actually a real-time strategy game, not turn based; however it reminds me much more of Civilization than it does of Warcraft/Age of Empires.
This is the buildings screen (be sure to note my wittily named village), and there are many of your typical buildings, such as a barracks for building troops, an academy for researching new troops/technologies, a blacksmith for upgrading weapons, and stables for cavalry.
Another familiar element is the hero. This isn't as big of a deal as it in games such as Warcraft 3; he gets to level up, and get stronger, but he doesn't get any cool special powers unfortunately.
To build things, you of course need resources. In Travian, there are two main ways to get resources. Firstly, you are surrounded by fields. There are wood fields, wheat fields, iron fields, and clay fields; fairly standard. As you upgrade your fields, you produce more of that resource per hour. The second way is by raiding other villages and stealing their resources.
There's no gameplay involved in the actual attack, you just send however many troops to your destination, and based on all of the attackers/defenders stats, the result of the battle will be determined. If you are 'raiding', each side will take one swipe at the other, then the attackers will steal as much resources as they can hold, and march back to their home village with their booty.
If you are just doing a normal attack, the battle will continue until one side has no troops left. If the attacker is successful, the remaining troops will take their bounty and return home. In either case, a defender can protect his resources by building crannies, which keep a certain amount of resources safe.
As with every strategy game, there is more than one race, group, etc. to choose from. In Travian, your three options are: Teutons, the aggressive, offensive folk, the Gaul, a tame, defensive tribe, and the Romans, which are a middle ground between the two. Another aspect of the game is alliances, but since I'm opting to stay solo for now, I don't have much to say about that.
I should clarify the phrases "time drain" and "longest Civilization game of your life". You only play it for a few minutes at a time, to set up building orders, send off troops, etc. I play for about 15-20 minutes a day, a bit longer if I'm doing a lot of attacks.
It's fairly addicting, especially if you know people in real-life who play, and can geekily discuss the game with. If you'd like to join me, I play as a Teuton on server US2, with my home in the NW quadrant. You can sign up here (this is a referral link), send me (randomguy132) an in-game message if you do, and I'll help get you started and answer all your questions and whatnot.