As of now, this is the most-played game in my Steam Library. I played this obsessively for a few weeks, giving up entire weekends to it. When you start one of these games, be prepared to give up the next 20 hours of your life, because that's how long some of these games can take, depending on the game setup (difficulty, world size, victory conditions, etc.)
The graphics, music, sounds effects, and gameplay all perfectly complement each other, and they don't get old even after hours of gameplay. Because you don't want to leave a game unfinished, you end up saying, "Just one more turn, then I'll take a break." Three hours later, you're still playing, literally starving because you can't leave the game to cook some food. The game takes so long because it takes time to build up your force enough to overcome an enemy. There are also neutral monsters which pose a threat. Not to mention, you have to wait for the AI to finish their turns. The wait is totally worth it, because the feeling of slowly overcoming your opponents is addicting.
The AI isn't super smart, which is good or bad, depending on your perspective. Personally, I liked taking advantage of the flawed AI strategies, like sending their entire army to me by boat, which I destroyed before they could even land. Diplomacy with the AI is somewhat of a joke. They might make a truce with you, but they'll break it on a whim. I tried to be honorable with truces, but after you've played awhile, you start to understand the motivations of the AI when they make a truce, and you can tell when they are about to break it.
Another great aspect of this game is the random world generation and fog of war. From the initial setup, you have an idea of what the world is like, but not the details. Curiosity and fear of the unknown helps to maintain your interest as you explore the map.
After playing this, I tried Civilization 5, and personally, I hated it. I'd rather take a history class. Personally, I don't like playing games that remind me of reality. Warlock is a fantasy escape into another world, and it really absorbs you. I can't recommend it highly enough.