Rover brought up some very good points. I started this game as an ACN and eventually became Summoner. I was vested in the job, but found it wasn't thrilling enough for me. My MAIN reasons are the following:

Role Limitation - This is less of a problem with the job itself and more a problem of SE's implementation of the job. This class is so freaking diverse, but a forced application of "DPS" is many times discouraging. This job is a jack of all trades, master of none type. It needs to be given the opportunity to use it's diversity, but SE has shoehorned jobs into playing ONLY the class they were intended for. With cut and dry classes like Tanks, that's fine. But support/multi-role classes like ACN/SMN/SCH/BARD get shafted with this type of implementation.