Viuuil
I don't really have a preference of gameplay, & My computer is...pretty good lol.
& it depends on the game.
For a game similar to WoW I'd recommend Tera. It's really action oriented and it has a decently high skill cap around the time you reach level 20. It has a high focus on BAM (Big a** Monster) fights. You can beat them alone if you're good enough but having a team always helps. The max level is 60, with 7 races and 8 classes. Great visuals and very flashy.
For side-scrolling beat-em-up action I recommend either Grand Chase or Elsword. Elsword is the spiritual successor to Grand Chase, developed by the same company, and a bit more fast-paced. The graphics are brighter and more colourful, whereas in Grand Chase they are darker.
In Grand Chase, there are currently 14 characters available (which can all be unlocked, starting with 3), and each one has 4 jobs (3 advancements). Some of them don't have a few of their jobs released yet though. Max level is 80. These characters are gender locked.
In Elsword, there are 6 characters which can each advance into one of two (three in korea) paths. Each path has two jobs to advance to. Max level is 60. These characters are gender-locked.
Dungeon Fighter is a decent game as well and really follows the old school arcade style beat-em-ups. Lots of class options there. I think the level cap was raised from 80 to 85. One downside to this game is that choosing the male/female version of a character slightly changes the play style.
For a real-time tactical battle system on a grid (action points, movement points, and 30 second time limit per turn) you could try Dofus or Wakfu. Wakfu is the newer game, both made by the same developer. They are really different however, in terms of character progression. Dofus max level is 200, while Wakfu is currently at 105. (Wakfu lacks a lot of content; I found the game to be extremely dry.) 15 classes to choose from in Dofus, and 14 in Wakfu. (Yeah they're the same classes, but they were changed a lot for Wakfu).
For old-school mmo and pixelated graphics, I'd try Trickster Online. It has a decent community, and the art style is nice. The combat is clicking around the screen to walk and using hotkeys for skills. 8 characters to choose from, 4 Male and 4 Female, 2 from each type of character. Charm (tank), Power, Magic, and Sense (the weird one that's good at crits, drilling, and has a bigger inventory space). Similar to DFO, your character does change based on if you choose to go with the male or female counterpart. Be wary, max level is 400.
