I have a friend that has the completionist attitude towards games, he'll complain every now and then about the grind of getting every last achievement trophy, I'm like "why even bother if it's a grind?" lol. I've never really been into RPGs or JRPGS so I don't think I've had that problem, maybe finishing up action games like Goldeneye but I think that's the only game I grinded out to get every unlockable character. I've yet to finish a Zelda, Final Fantasy, Phantasy Star, or a Xeno game since I lose interest about 3 hours in. Growing up I loved beat 'em up (Streets of Rage, Batman Returns, Double Dragon), fighting (SF/KoF/SC/GG), or racing games (Top Gear, GT, Al Unser F1,Forza), and these aren't very long games (beat 'em up) nor do they have a definite end (most fighting & racing games). PvE PSO is pretty tolerable for about an hour because to me it is just a beat 'em up game with no real depth or story that you can just log into, kill shit, and then log out.
The PvP aspect of games are what I love and I can still play PvP PSO, fighting,racing, or basketball games for hours and hours until my hands start to hurt loool.