The Guild 2 is a good game, good time this to pick up the Renaissance standalone expansion.
As for what it is, Sims meets Fable, not really. I would say at its core it's a business simulation, you advance your business ventures and with the wealth you gain from that you can try to gain influence and political power. I would say it's a bit like the Patrician games except smaller scale, more focused on the production side than the trade side and with more RPG elements. It's pretty fun to develop your businesses in such a way and to mess with competitors through both legal and illegal means. I will warn anyone though that it's not without flaws, it's got a certain degree of Eurojank to it. If you're used to that, it'll be fine, if you're not, you should probably skip it.