I felt that it is truely a multiplayer game... I could see it get boring very quickly on solo... I enjoyed SSE to a degree, but it also felt a bit like a chore... (maybe thats just the first time around) I got annoyed with all the repetative little creatures they throw at you.
My only other problem with it is that there are so many damn characters, i feel like I will never settle in and find a favorite (im a bit overwhelmed)
Nevertheless, i give it a 10/10, surely more entertaining then SMG.