It seems to me that modern MMORPGs are based on Achievements. You grind to level up, you grind to get gear, you grind grind grind to achieve goals set forth for you by the developers. The problem is, with all the focus on carefully balancing those grinds to take as long as possible, MMO developers seem to have forgotten to make the games fun.
The thing is, I'm not that driven by achievement-based gameplay. I've never cared for the most blatant form of that: achievement points. But the grinds past that don't really interest me either: questing to level up is a bore, grinding Instant Action for PA levels or Inscribed Sourcestones to unlock a useful ability or buy a useful piece of equipment is a pain, and sitting around week after week to do one raid run is downright upsetting.
Another thing that's bugging me in Rift is the lack of gear inheritance to a number of key game facets. For example, if you play a Warrior, your HP goes up as your gear gets better. But if you play a Mage, while your HP also goes up, the HP for your pets remains unchanged. So when monsters get tougher to provide challenges to the other three classes, Mages can't stay relevant. And in raids, I play an Archon, and many of my abilities provide fixed bonuses. +360 damage was cool when people were hitting for 360, but now that people hit for 1360 my ability feels lame. Trion needs to incorporate gear scaling to ALL abilities, including pets and buffs/debuffs.
I think what I really want to see in Rift is the PvE equivalent of Planetside: trying to conquer territory for no reason other than the pure fun of it. Fight off invasions to defend wardstones, take out enemy strongholds: basically, their world invasions on a much more meaningful scale. Crucially, I don't want it to ever stop. I want to be able to log in any time and instantly jump into that action. So, yeah, combine instant action and world invasions and produce something that focuses on the fun of the gameplay experience, rather than the rewards you obtain for participating.