The onus is also on the developer to make the game accessible at any point that somebody should decide that they need a break. As in they're able to pick it back up, and pull something up that gives a quick recap of wtf is going on. Having lulls in the story is a good thing, it provides the player a moment to breathe.
The issue here is that that ME2's story/gameplay design left it so that the main story was very minimal in comparison to the various sidequests. You had 5 "story" missions (intro, previously stolen colony, Colony being stolen, derilect, and finale) but 8 side missions that were each as big as a story mission. This may just be me but I'd think that the story should take up more time and gameplay than the "gathering your friends" segment of the game.