Well, I haven't left FF14:ARR yet, but if I do lack of larger group content will be near the top of list of reasons why.

I heard 24 man raids when the game was being hyped before release. Now we get some stupid alliance stuff? That doesn't cut it. Not even close.

Honestly, 30-36 player raids would probably be nicer. But 24-man not so bad. You want a large enough number so that there is some flexibility - like 4-6 slots can be different classes, or even sometimes empty if you're good, and still win challenging fights. This is necessary so that you can build a guild (FC) and still function when a few people aren't available.