I did all of Demons Souls in single player. I only got invaded once and only summoned one guy into my game. On your first play through (and in my case, only) it is best to be phantom most of the time anyway which stops nearly all online stuff anyway. Dark Souls is a little more online focused, but again, I tend to stick with the offline. It will certainly be quiet without all the messages and ghosts running around though, I took some comfort that other people were struggling through 'with' me. Still a fantastic game. I'm still struggling through Dark Souls.... I was getting owned in darkroot garden last time I played.