This is a great foundation from which they built 3, it does however just feel like a foundation. There isn't much to do besides the main missions, and although there are military bases and outposts you can destroy like in 3 the game doesn't give much incentive for doing so in this game.

To summarize it's a precursor to 3, if you aren't playing through the whole franchise and are instead just checking out a nice sandbox third person shooter with lots of explosions I would go the 3 first