How'd I know that coming into a thread asking for a RPG, Aurora would be here bashing a perfectly fine game. For a game you dislike so much, you can't seem to stop talking about it If its not Asian and doesn't require an incessant amount of grinding, Aurora hates it.
Im enjoying seed right now. Actually a really good game but has potential of beeing somewhat of a grinder in the later levels. Time will tell. Its a good game non the less.
Nobody mention Undercroft? That is my favorite RPG on iphone. It is turn-based and you control a party of 4. With multiple characters, you can mix and match different classes and skills. I think i prefer that over solo rpg. And you mentioned playing on bus? I think turn-based will be better for that. Now i am playing inotia 2, which is also very good. Here we can control 3 characters.
Inotia2, Seed1, Dungeon Hunter, Ravensword(may not count), Underworlds, Undercroft, Zenonia; they are all good. Inotia2 is currently the best in my list