In no particular order:
MapleStory is a fantastic game, but is one that oddly requires a decent computer and even with that you will lag in congested areas. The oddly shaped head characters and the many unique monsters in it make it a fun game. The side scrolling platforming setup is a welcome setup to the MMO setting, but it can have it's tedious moments. I personally have yet to play recently so I have no opinions on the Pirate class, but the game as I remember it required teamwork to effectively push far in it. Or just alot of free time. With a max level cap of 200 and plenty of quests, this game will keep you busy for as long as you're interested. Not suggested for the not so dedicated unless you're willing to hunt down and setup for an unofficial setup.
Ragnarok Online was essentially 'My First MMO' for me. It still holds a dear spot in my heart and I return to it every so often. The game is very basic but is also charming and addictive as well. With many classes and more generations slowly coming out as well, you'll spend lots and lots of time on it trying out every class and setup. Though the official server has a free setup, the exp rates are dreadfully low. I personally suggest trying out an unofficial server as they can have much more fun, but may be more tedious to setup. All in all it's a charming game either way that I would suggest you give a shot at.
One of the games on the higher end of the graphics scale, this is an interesting game all in all. Megaten Online allows you to have a constant companion of what you chose, depending on your own level. As you get stronger, you can catch or create monsters up to your level as well. There is also an alignment system as well that affects story, companions you can get, and various other things. Weapon variety is pretty interesting. Pistols, Shotguns and (sniper) Rifles are all very potent weapons but you may run into demons who can bounce back your shots, which then you'll need to use Swords or Blunt weapons (I forgot what else there was, I was a gun user myself). Very interesting game with interesting setup. I'd suggest trying it out if you have the time and like the Megaten series. (Persona, Shin Megami Tenshin)
Mabinogi, my recent most addicting game. This game has alot to it that can make someone stick to it on a long term bases. You don't even have to play constantly to get far, now with free rebirths (at age 20 ingame). There are three ingame races; Humans, the basic all around race, Elves, the speedy longrange race, and Giants, the powerful melee fighters. When you start the game for the first time on a new account it's suggested to use a human first and earn freebies of the other two races so you can try out all three. Though you are free to make any of the three with your first card, you wont be able to get the other two if you pick an Elf or Giant. The skill system can be pretty tedious but its why I say this game is a long term game. It'd take me forever to explain just how much is in this game, but I'd really suggest anyone who hasn't to try it out if you can and see if its your thing. There is just alot to do in the game once you get into it.
S4 League, one of the only non-rpg online games I really love. I know a bit of you have heard/played GunZ before. It's essentially that with anime style mixed in and the pro stuff taken out (K-styling coughcough). You can play this game with putting a penny of your own money into it if you do good enough. Levels are not really needed for anything except equipping a couple of gear that you wont really need. Plus you can get a freebie of everything in the game by doing a license test for them. I believe all demo items last 3hours of ingame use. This gives you enough time to try out everything as well as build up PEN (ingame money) to permanently buy or buy another demo of a specific weapon you like. Very fun and fast action paced game to break the pace of the regular mmo dealie.
Now that I have shared my personal favorites, share yours as well so others will know they exist and may join you in them as well. :3
-wasboredwhenmakingthisthread.w.a-
