I think something we could really use in FFXIV is truly challenging content. This does not entail time spent waiting for a spawn but rather something that requires true player skill to beat. Maybe the future battle changes will remedy this but our current content is far too easy. I'm not asking for this to be implemented immediately but I'd like to see them try to keep challenge in mind when designing future content.
Things like bosses, NMs, story quests and dungeons should be challenging for players in the rank they are intended for.
Especially for endgame content, things like this should require a full group of 8 and should really test your skill and endurance as a player. Your group should have to have a plan and be well coordinated to win. There should be difficult, down to the minute fights that have you on the edge of your seat. Challenging content like this is extremely satisfying to overcome and most importantly, it's fun. Afterwards you have a sense of accomplishment.
This doesn't necessarily all have to be about stat values and straight fighting, unique content can also be challenging. A fight that forces you to constantly adapt to a changing situation is challenging. A fight that requires you to use something other than traditional battle tactics can be challenging.
An example of a fight that is unique, fun and challenging is the Jhen Moran fight from Monster Hunter (when you're not obnoxiously high rank). You're on a boat, this monster follows alongside the boat and moves around and attacks from a range.
You have to be mindful of what it is doing at all times as it's attacks are incredibly powerful and if you don't know what you're doing you will die quickly. It can ram the boat, to stop it you have to hit a gong as it is sensitive to loud sounds. When it's out of reach you have to man the ballista on the side of the boat and shoot at it. When it comes close enough to the boat you can jump over onto its back and do some serious damage but you have to jump back to the boat before time runs out. When it makes it's final approach before the second phase someone has to use the Dragonator with precise timing to pierce it's chest as it jumps at the boat. The second phase is a straight fight and usually comes down to the minute, your team is giving it their all to get the kill.
Something like that requires team coordination, proper timing and makes you adapt to a constantly changing situation. When you beat it, especially for the first time, you have a real feeling of accomplishment.