However, I've since changed my mind, and did so because of Dragon Age. Not only was it a great and modern game, but it really felt like playing one of the old Baldur's Gate titles. It wasn't just a modern re-imagining, it really brought back memories of the others.

Given that, I definitely don't think old games should be left to rot.

To actually answer your question, I'm going to say Sim City, because it was more or less a one-of-a-kind. There haven't really been any other major, big budget city-planning games. Admittedly it was something of an unusual niche genre, but I really enjoyed it, back in the day. And I think it's something that could be modernized easily. Not only would it be easy to retain the same feel, as the base gameplay could be more or less the same, but really great things could be done with modern connectivity and processing power.

Anyway, I think twould be cool. /nod