I just beat both Dragon Quests I and II recently using the translation patch of RPGONE and this is my experience.

Dragon Quest I:

Being the first in the series it is expected the gameplay is bare bones but still does the job. Since the translation follows the Japanese names it is confusing to check guides that are based on the North American localization for some hints on what items do in the game. Nonetheless, the game is flawless until the dialogue of the King Dragon (Dragonlord in the NA localization) after you beat him and turns into that dragon form is garbled a bit. I hope this gets fixed. I am unsure if it has something to do with the emulator but I hope the translation team is still open to checking some bugs.

Dragon Quest II:

Quite a jump from the first game in terms of innovation. Still following the Japanese names and not the North American localization (which is not a problem and, again, makes it confusing to look at game guides). Unlike the first game this had a number of bugs. The most gamebreaking of them all is when the Prince gets sick at an Inn in Beran however I never experienced the bug (check redtrollinhowser’s review to ensure you do not encounter it) which is fortunate for me. There was one bug which put me off and that is when you are in the Sea Cave the graphics of the map especially in the lava sections become distorted. At first moving from one room to another fixed the problem until it eventually didn’t forcing you use the Outside spell. Fortunately, I got what I needed from the dungeon and beat the game but I hope this gets fixed, too. Also, I am unsure why the Prince reappears at the town where you first met him even when he is already in your party. I do not know if this is a bug or if it was already in the game even before getting patched. I simply ignored the Prince because it felt that I might trigger a bug.

Overall, the experience playing the translation is fun. The bugs are not going to stop you from beating both games but not knowing these bugs especially for the second game might make you lose precious hours spent.

I hope RPGONE can take a look at these bugs and if possible (well, this is wishful thinking on my part) they create a translation patch using the North American names in game but still retaining the Dragon Quest title.