Apologies for yet another free iOS post, but Gamevil’s one of the more respected mobile developers out there with mobile hits like Air Penguin to their name. And, while there are tons of Korean Action RPGs in the App Store, not many of them are free.
Fair warning, Advena does have a “secondary currency” called Vena points that costs real world money. Gamevil’s got a solid reputation for not gouging their customers, so it’s probably safe. Still, your mileage may vary.
I haven’t played it (aside from starting it up to grab some screens), but App Store reviews range from “cool” to “kool.” So, chances are it falls somewhere between one of those two.