i have played a lot of the free mmo's. honestly only a few have held my attention for more then a few days. MegaTen however is a really neat mmo. what makes it special is the demon pets. you can tame a demon and fuse it with another to make a different demon. and on top of that you can have it inherit some of the skills of its parent demons. this makes for a lot of fun. best pet system i have seen in any mmo.
the story line will keep you busy for a good amount of time. then the side quests are all over so you don't know who you should talk to. me? i talk to every npc just to make sure.
the skills system is nice also. you don't have a set class. you pick what skills you want to lvl and go. i am a gunner with a minor in demons. i have a alt that is a mage with a minor in guns. but you can make your character how ever you want.
btw. this company has a lot of other games also. so go take a look. you wont be disappointed with megaten. its a lot of fun.