SR3 was a pretty good open world game, or at least it was at launch. It doesn't hold up super well now in my opinion. Since the game was being built on an updated engine with new animation systems, etc, a lot of what was built in SR1 and 2 could not be reused to save on development costs. So the scope of SR3 is smaller in a lot of ways when compared to SR2.

Also, as someone who worked at Volition for a while, the reason why all future SR stuff was more like 3 and less like 2 is that 3 was the franchise's biggest seller. The people that really wanted more SR2 type stuff routinely showed up as a very small minority in user and market surveys, even when there were explicit calls for the fanbase to rally and really make themselves heard. That's sadly the reality of the whole thing.