You should really look into Atlantica Online. Played this game for about 2500 hours (Including nighttime trading though xd) and it is the best mmo i have ever played.
The pve and especially the pvp is very interesting due to the gameplay being very strategic. You get 3x3 spaces for your mercs and your main class to play around with. The mercs themselves are very unique, although it comes down to melee, magic and ranged. You have guitarists, cannoneers, shielders, spearmen, monks, shamans, archers, powersaw and whatnot. There are so many combinations you can try out and if you switch around a lot, which you should, it's really entertaining for a very long time. Of course there is a grind element but imo it never got boring. Especially with the new siege-mode, where you have your mercenaries and you move them around with your buddies trying to kill of all enemies in an area, destroy certain buildings, upgrade your own, well kinda like a MOBA only against bots, no more 3x3 just a nice big ass chessboard to play on. And teamwork is really required in those dungeons and the normal dungeons, because otherwise you will fail. Graphic is outdated, but who cares, we all play warband, don't we? =D
http://atlantica.nexon.net/The only downside is that players who are willing to buy a lot of store items really kick more ass in the pvp mode that is the most popular one. They also introduced a pvp mode that doesn't include armor upgrades and whatnot, but you don't get too much profit out of that. I payed a couple of hundred bucks like 5 years ago and last time i checked it out i was a poor basterd. I was lucky i didn't sell all my mounts and $$store items so the inflation didn't really harm me too much, but the prizes can really scare you if you are new to the game.
However, the rewards of guild dungeons and nation dungeons, as well as the new siege dungeons are pretty insane. It's a long way to get there before you can spend billions of cash to get one of the more fancy mercenaries, but once you established that it has an awesome endgame, although grindy. But then again, i've never really seen the grind as a grind, because of the very entertaining battle system.
Basically it's one of those games you either hate or really love. I loved the likes of FFVIII, FFIX or The Last Remnant so this game really got me hooked. And to be honest, writing this post about it really wants me to install it again xD
