To see the major fault lines, think of things that even your own groups don't want to do the same way. If there are things you want to do some times and not others, you can bet money that there will be groups that prefer one or the other almost exclusively.
For me, one such example is the degree of emphasis on tactical fiddly bits and/or the grid. Not that I can't work around it, because I can run 4E off the grid more than I do on. But unlike, say, the very pleasant experience of 4E adventure preparation, running off the grid is something that I have to work at. And it is something I bring from my own experience, not something that is really explained well in the game. And really, this isn't even by campaign or a dislike of the tactical fiddly bits. When you've got a huge boss fight at a key moment in a campaign, those can be fun even for people who otherwise don't care for them. But getting an important but not crucial fight handled in 20-40 minutes is also fun.
And then I read what other people say about this topic and see pretty impassioned pleas to have tactical fights on the grid and equally impassioned to not have them.