Aw man, I remember playing the first Dark Cloud for PS2. It was such a good game, but I unfortunately never got to finish it :/

Hmmm, I dunno if this genre is necessarily underrated, but a lot of people I know did not know about Dynasty warriors/Samurai Warriors. 
Also, I really like the Tenchu series :3 

TERA is also a really good, free, online MMO :3