Far Cry 2. It could be a good game but I couldn't make myself to play it because of two reasons:
1. Malaria. This hits you before you can say "open world".
2. Ugly. It takes the "Brown is real" concept to new grounds with 430% more bloom. Shadows are too dark and edgy.
http://img545.imageshack.us/img545/6922/farcry22011042803291602.jpg
It was a beautiful game with a fairly deep map creator.
It was also extremely repetitive and incredibly large to traverse around. Normally that wouldn't be a problem but the lack of architectural and geographical diversity, mixed with the respawning enemies that'd constantly be slowing you down made for an incredibly sluggish game.
If you want a game in similar style, scale but over all just more enjoyable and possibly the same amount of content (if not more) for the price point, consider purchasing Just Cause 2.
I would recommend Just Cause 2 as an alternative to GTA4. Try Stalker as an alternative to FarCry 2. (Just Cause 2 is still awesome though.)