I just got my HTC M8 a few weeks ago, and I just happened to do extensive research on great RPGs available.
Ravensword Shadowlands is a Skyrim-style RPG, and it plays great on HTC M8. 7 dollars on both google play and amazon app store.
I haven't played it but Dungeon Hunter 4 looks pretty good. I have played the 2nd however. Dungeon Hunter is your basic dungeon crawler from Gameloft. It's a good game series (other than the 3rd installment) with great graphics and pretty good gameplay for a mobile game. It's also free.
Also SoulCraft is another good RPG with solid graphics.
Chaos Rings is a series from Square Enix is a JRPG, kind of like final fantasy, with high end graphics. I think most of the games are over 8 dollars, but sometimes you can get them on sale for half off.
If you're looking for something with more 16-bit style graphics:
Zenonia is a great series
Inotia is good, but IMO not as good as Zenonia
Illusia 1 and 2 are good if you're looking for side scrolling RPG.
If you really need more, developers Com2uS USA (Inotia and Illusia) and Gamevil (Zenonia) have even more RPGs avalable, as well as other good games. Best of all most of them are free, unlike when I got them a few years ago on iOS.
Also check this out:
http://www.androidheadlines.com/2014/10/featured-top-10-best-rpg-games.html
Also the M8 is one of the most powerful smartphones on the market, so I'm extremely confident that it could handle Dragon Quest. But unless you're a die hard fan I wouldn't spend 20 dollars on it. But that's just me; there are so many other games, and a lot of them are free.
Been away for a bit, but sneaking back in.
Gaming on: PS4, PC, 3DS. Got a Switch! Mainly to play Smash