Phantasy Star 3, the game I am playing now, has one route that is rather short by RPG standards, yet doesn't seem to be especially difficult (though I might not recommend this route on a first playthrough):
1. Play through normally until you reach Cille.
2. Buy an Escapipe (if you don't already have one), and give it to Mieu or Wren.
3. Go through Cille and defeat the king. You will be asked who you want to marry. Choose Lena.
4. As soon as you gain control of Nial, use the Escapipe. You will end up back in the Cille dungeon (which is not intended to be reachable at this point).
5. Go through Cille again (the only enemies you encounter will be Chirpers, who are really easy), and kill the boss again. This time, choose to marry Alair. (Choosing Laya will put the game into an unwinnable state.)
6. The third generation starts. You will need to get certain plot critical items that you didn't get as Nial, but otherwise you can proceed as normal.
This game, which was originally for the Sega Genesis, can be found in various collections.