It also helps to play on a cohesive goal-oriented team. It's always been the people I play with that keep me going.
When the goal became "do everything on hard mode again to level for Tundra", my entire team alongside myself decided it was off the shelf until they add all future levels + new weapons and re-jigger that grind portion since its obviously making up for lack of content currently.
Theres also just not enough gameplay to keep me entertained. Had all the photon arts for my melee weapons early on, thats about it. Graphically the game feels like a baby step beyond PSU.
I'd been meaning to go back to Vindictus, especially now its got that wealth of 2 years of content, but even then the base package and before all the additional I remember it as an action packed take on the PSO like formula, tons of varying looking loot/armour, and some pretty damn sharp graphics. When Evie and magic soon came in, that made the whole thing a full title in the area, and that was a fair while back. Obviously theyre still adding stuff like the bruiser character and the absolute newest archer character, but as something that was fun to play and a fresh feel on the genre it cannot be rated enough. Even the grindy portions to get more points in a quest have interesting different approaches to gameplay attached such as finishing enemies with sub-weapons, items, kickings and varying difficulty levels from the start. PSO2 just has speed runs.
Sega's misstep with PSU has neutered them however into this "just PSO1 again please, different paint" position that tickles a retro itch but doesnt take the genre or gameplay to anywhere different since essentially photon arts in 2006. Worse still, the opressive atmosphere that made PSO ep1-4 feel so alien is completely missing while PSO2 is more an extension of PSU's anime-tacular awful approach.
The longer I leave PSO2 though to go back when the content is there, the older its going to feel. Korean developers and Capcom with Monster Hunter have really conquered this space while Sega had it's pants down.