I played with three completely new players today, and one old player, so there were five of us. These three players had NO experience with this sort of game whatsoever, so it was crazy going through the basic rules, and walking them through everything. I've never played with this many people before either.
They complained that there weren't enough clue tokens on the board, as one clue token is placed during the Mythos phase at a time, and all five of us had picked up all of them rather quickly. Still, I think things started getting tougher and more interesting later on as monsters started to move and more gates started to appear.
I guess the game can be slow with 5 people, and some players felt like they couldn't do much...
At least for one full turn (all phases).
Overall I think it went pretty well. We didn't get to finish because they had to take their kids home, but they enjoyed it.
Have you ever had to teach completely new people the foundations of this game? I was almost as overwhelmed as they were.