Other than Quest or Undercroft, there really isn't a "deep" RPG, and I doubt one will come anytime soon. It's a handheld device after all. There are a million J/KRPGs all with the exact same gameplay - NPCs that give you quests like "kill X number of Y and get a reward of Z", and there are those J/KRPGs that try to mimic console RPGs by providing great graphics but the gameplay is still way too simple to be qualified as console-quality or "deep" (Chaos Rings, Eternal Legacy, Infinity Blade), more like a "test drive" of various scenes in a console game. Later generation devices and iPad are perfectly able to handle great RPGs like the Tales series for consoles, I don't know why so far no developer even attempted such a proper RPG yet. Tales of Symphonia had horrible graphics, but its huge amount of content, moving story, and wonderful music kept me playing for like 10 playthroughs. Chaos Rings might have great graphics, but it is nothing more than a simple turn-based dungeon runner with nothing else to do.
Sure, you won't find any sidequests in Chaos Rings; it's about as linear as RPGs come, but it's as good or better than almost anything on psp. The storyline is told through multiple perspectives and playable characters too, which is awesome.
Inotia 3 is a great KRPG. Whatever you do, don't but eternal legacy lol. It took 8 hour to beat, but I honestly think playing it redefined how a game could be this much of a chore. The first 4 out of 6 chapters were pretty decent, allowing me to prefer it much more than chaos rings. The graphics were nice, the sound wasn't bad (except the voices...my god), and the gameplay/combat was very nice since it's pretty much an open world in a way and the combat was quite different from other turn based JRPGS. However, upon reaching chapter 5..battles suddenly began taking 5-10 minutes and often there were no save points in between a series of these lengthy battles..so dying really sucked and probably added at least two hours to the total playtime. The magic/equips are pretty lame since normal attack does more than 'special' attacks often and equips are..limited to say the least. Sadly, it gets worse, ending with probably the poorest conclusion seen so far in any RPG on the iOS. I have never been so disappointed, especially since it was a chore to play through to begin with, with an ending. I mean, the credits didn't even roll. That's a first for gameloft, but I can safely say I don't want anymore single player games from GL after this..and I've been a faithful customer since the first Hero of Sparta..2 years back. On the bright side, I now have 770 mb free instead of around 100 mb on my 32 gb. More games, wee. Sorry for the wall of text.
As far as iPhone RPGs are concerned, nothing comes close to Inotia 2 in terms of the game battle mechanics (full real time party control), skill tree diversity (tanking, healing, damage, area effect, range specs). I haven't had much experience with Inotia 3 yet but so far it looks like it's just as good, if not better than its predecessor. While the graphics aren't as sharp as it could have been, however, the game's wonderful soundtrack and better written game script really does make up for it, IMO. It's superior to Secret of Mana in just about every way. Zenonia feels like a kid's game in comparison. Do not mistake Inotia 3 as a typical KRPG, because it has a lot more to offer than that. Aralon though having above average battle mechanics, however is still not even in the same league as Inotia in terms of combat. DH2 is even worst than Zenonia (look, everything dies in one hit pretty much).
