While Fiesta online is fun initially it eventually becomes lack-luster because it doesn't initiate anything new to the MMO genre. Classes, fighting mobs, quests, a semi-intriguing story plot that isn't as deep as I'd like it to be. xD It's nothing news to me after being an MMOer since I was 14. It was cute, but it was really nothing different from Ragnarok, Trickster, Ether Saga, etc.
I suggest right now playing Vindictus. <3 It's a dungeon crawler MMO that is heavily story based. It uses Valve's Source Engine (which is amazing and the first MMO to use it) and makes grouping with others optional. It's also free to play which is nice. It also won 6 awards. (link) Which is amazing in my book. >_>