One of the better Korean grindfests out there, unfortunately that's not saying much, and the devs are ruining it.
Side note: many of these grindfests COULD possibly be great games; however, the proliferation of hackers, botters, farmers, and just plain cheating griefers make it very unlikely that a well-meaning, FUN-seeking newcomer will be able to "get" into the game. The fact that I point Flyff out as not being so infested should tell you that you don't have to worry about that junk ruining your experience.
Story-wise, Flyff is nothing special. Even the flying ability is gained automatically upon reaching level 20 (there used to be a quest, but it was taken out - why?). The great majority of the quests are fetchquests which, 95% of the time, require you to kill X number of Y monsters. Nothing special here, and, sadly, nothing to make Flyff particularly memorable.
Tech-wise, Flyff looks fairly nicely animated, giving it a quaint almost anime-like feel. There are 4 base classes, which in turn can each branch off into 2, leading to 8 total classes. Everyone starts out as a vagrant until level 15 for the first class change, btw. Also, you can select your gender regardless of class during char creation. Sound effects are standard fare and serviceable, music used to be pretty good although one of the recent update bugs made combat music not play (although the mp3s are still in the music data folder). The only people to complain about the graphics would probably be gfx-whoars who would be better off playing FPS-type shooter games anyway. Jeez, be more appreciative, people. The graphics and sound effects make up the atmosphere quite nicely. The spell effects are pretty nice to watch although they do get repetitive after a while, can't help it in this kind of game.
The official forums are pretty structured and well-maintained, with a constant GM presence, so things aren't flame-filled free-for-alls like I've seen in other games. Good source of information too, with to-the-point sticky threads containing almost everything you need to know.
The game itself... well, it's a grindfest. There are 120 levels, and after the latest update now you can de-level from 120 to 60 and repeat the climb again at half the exp gain rate, in what is known as the 'Master' quest levels, and upon reaching 120 again (this would technically be level 180) , you can do a capping 'Hero' quest. However, the exp gain rate is pretty fairly low; it's quite fast going from 1-60 (all the way up to the 2nd class change), but around there it's already started to slow down quite a lot. Despite being more than 2 years old, there are only a handful of level 120 players.
However, it is possibly more the result of people getting bored, rather than from lack of trying. A good player witth support can conceivably start a new character and be in the late 30s in a single day, and make 60 within the week. Even as high up as in the 80s, it's still quite possible to level once in a day, provided you do nothing else. The problem is, even despite the large Flyff gameworld (you don't load areas, only for the dungeons), and the variety of mobs (below 60 you very nearly which change mobs to fight each level), there IS nothing much to do except grind.
The equipment system suffers from the usual linear progression problem (i.e. the 'wood sword, to stone, to copper, to iron, to steel' problem), although items DO occasionally spawn with stat-bonuses, e.g. a helm that adds 2 to your Strength. Thus everyone eventually aims for statted uber equipment, instead of 'merely' plain uber equipment.
The game uses the F2P + CS model (free to play, but with Cash Shop), and contrary to many games actually allows the trading of premium items, which results in many players buying stuff from the Cash Shop to resell to other players for in-game money; not a totally bad thing, and in fact I think it's a smart dev move, it allows people who would not spend money on the game on principle (e.g. Yours Truly, since I feel they don't deserve the money unless they fix some old and glaring balance issues) to eventually get our hands on CS items, as well as encourage players to traffick in said items for a profit. Everyone wins. I mean, if they were untradeable, who'd want to buy all those ugly Cash Shop outfits right? But since you CAN trade them, some guy is probably gonna buy them because he can then sell it off to someone else when he gets sick of it.
A quick word on the player base, no cheating and no lame free-for-all pk makes it nearly unique among similar korean grindfests, which basically translates into most people are nominally friendly upon greeting (instead of jumping you like in other games). Sad that this alone means it's a great game, compared to all the other turds out there.
Check out the general forums, flyff-forum.gpotato.com, for a more in-depth view of the game.
This game is only slightly above solidly average, and the fact that it is nearly almost the only korean grindfest port that ISN'T overrun by cheaters makes it worthy of consideration.