I would say the biggest advantage of multiplayer is replay value. Once I finish and R&C game, especially if that includes the challenge mode, I might pick up another game for a while and not return to Ratchet. If there was a dynamic multiplayer (for example, COD has almost infinite replay value in multiplayer) that was separate from the story, it would keep players coming back to play it, especially because of the low time commitment (a multiplayer match might be 10-15 minutes as opposed to playing the story for a few hours). The way this fails is when people don\'t even look at multiplayer, the same way some people disregard campaigns in COD for multi or zombies. I never used multiplayer on UYA or RD (partially because it was 2006 and no one was online) but it didn\'t seem very appealing compared to the story. Because Overstrike is a new game and not a sequel, people will be more likely to check out all of its features and try out multiplayer if it is included.
The best sandbox game I\'ve played so far (not that I\'ve played many) is Just Cause 2. It is a little repetitive, but there is still a good variety of environment. Because of the quick ways to move around (grapple + parachute and hijacking), the creative ways to cause chaos, and just enough differences between locations, this sandbox is successful. This might be difficult to pull off with a 4 person coop, as each person is able to wander off and less likely to cooperate than in linear gameplay. It might be best for Overstrike to leave out sandboxes for this reason.