Dragonica is a free-to-play 2.5 dimensional side-scrolling MMORPG.
Dragonica describes itself as closest in style to MapleStory. Actually, that's selling itself a little short. MapleStory is a 2D platformer at heart, and Dragonica has very little platforming. Some of the later levels have you jumping from one small platform to the next, but the inclusion of an icon on the floor under your character removes any of the guesswork about where you'll land. It's more Golden Axe than Super Mario.
It's also a more fully-realised and good-looking 3D world. It's a bit of an illusion - you're mostly limited to left and right movement, with backwards and forwards adding stripes of literal depth to the combat. Meanwhile, exploration is made a little less linear thanks to the Hyper-Jump pads, which spring you to another horizontal stretch of terrain. It can be briefly disorientating, but it would be desperately boring without them.
The combat works simply - enemies are either on the ground, stunned, or flying incapacitated through the air. On the ground, they can be chipped away by your basic, no-mana-cost attack, blasted with a strong attack on cooldown, or launched into the air with your class's special attack. Once you level up, you'd be well advised to invest in an attack designed for enemies in the air; it's a game basic, and will let you decimate the enemies while they're airborne and harmless.