As for Megaten Online - who'd have thought even MMORPGs could be innovated!? Atlus and the Megaten team're actually starting to scare me... is there anything they can't do?!
Basically it's a mixture of vanilla Megaten, Kuzunoha Raidou and it's own new style:
Exploiting weaknesses stuns the enemy for a few seconds, and you have to make good use of a combo/ counter system in order to win battles by knocking the enemy back, knocking them down or putting them on guard "whiff" (Really, really refreshing in an MMORPG). The system effectively allows you to fight enemies at a way higher level than you and win with minimal damage sustained 8-). On the other hand, if you get mobbed, well... it's over for you even if your enemies are at a lower level (Think near permanent stuns if you panic and fail to react quickly enough). It really is a breath of fresh air for MMORPGs, can't believe I forgot to mention that.
Coupled with in-game cinematics (just love the boss intro/ death scenes) and the ability to negotiate with/ recruit demons during battles and scripted encounters/ scripted dungeons... well, it makes for damn fun levelling and a damn good MMORPG.