Lineage II was the same, albeit without having to pay for new chronicles. You'd play for months in an attempt to keep up with the cheaters (who NC never really did that much about despite protestations to the contrary), get bored and leave for a bit and get left behind. Still, it did progressively get easier to grind to high levels even solo, but it was always best in a clan.
I liked Aion as well - great visuals, custom look items, very nice music, and pretty different to L2, but fort sieges would go past at 10fps on numerous occasions. The sheer number of quests keeps things interesting, and it's not that difficult to get the items and experience you require, but it does require a decent measure of working in pick-up-groups... and they're usually not without incident. Additionally, like with L2, there's issues with character balance, but not quite to the same degree in that you feel punished for rolling a support toon.
I paid for two accounts for a good period when I played L2 (£8.99 apiece) then quit and only played the one in Aion. Might revisit either of them in the future (I have since they both went P2P) but I guess that, with MMOs requiring so much time, I may not have the time available.
Never played WoW, never wanted to. L2 players generally saw it as too cartoonish and "carebear".