I concur with the post above. The game breaks more often with each addition than it stays stable. It has difficulty using threads and multiple cores, as the game had been conceived when those concepts were just concepts, and the technology wasn't available. It also has primitive shading techniques that complement the old, cartoony and washed out look. No global illumination, no individual light sources, limited use of reflective surfaces, no parallax mapping. The movements, idles, and animations are also pretty bad.
These 'faults' are the results of negligence and developmental oversights on behalf of Ymir/GF. They could easily be overlooked if the combat system had a robust foundation to stand on. They implemented a poor hack & slash combat into an MMO whose engine doesn't support such a complex system. The game executes most action on the server side, and the game gives unfair advantage to those who have more stable and faster internet connection, or cheat.
Let's not even get into memory leak issues. :kappa: The game is still fun, though, and I treat it like a social hub. A hack & slash, action RPG Club Penguin, a bad one at that, too.