Yeah went through RE5 solo. Just too hard to get co-op coordinated lately. No one joined in me. I think it allows drop in and was set to allow randoms.
Fired up RE6 this morning and maybe 10 mins into the game (just after the opening credits) someone dropped in. Towards the end of my time playing two others dropped in as monsters as well. I think I got near the end of the first chapter/section when my co-op partner died and I had to get ready for work.
So far it seems pretty cool/fun. I never really played Resident Evil games before so I don't care if they aren't canon or properly connected to the older games or whatever RE fans hate about this one. Still early on so maybe I will change my mind but so far so good. Last time I bought it on PS3 (or maybe 360) I watched my nephew play for an hour and just never felt the need to play it myself.