This is my first post on this forum despite being a lurker for two years. Anyway, these are my choices from the RPGs I've played through:
1. Dark Cloud 1 and 2: They had great gameplay mechanics and I love these games to death, but the story is pretty forgettable.
2. Final Fantasy VIII: I love this game more than most of its detractors, but the story is pretty incomprehensible and contrived.
3. Pokémon: I don't think this needs explanation.
4. Star Ocean 3: Amazing sense of adventure and great gameplay, but the story left something to be desired.
5. Xenosaga I and III: I admit, I couldn't play through Xenosaga II because it was so unbearably bad. In any case, Xenosaga I and III had good battle systems and excellent minigames, but even as someone who has read Nietzsche extensively, the stories are incomprehensible. The games also lack the sense of humor and strong characters that made the story for Xenogears enjoyable in spite of its similar inability to make any sense whatsoever. I admit, I have never played through Xenoblade Chronicles, so I can't offer any judgment on that game.
I will note that I didn't include games that had mediocre stories if they managed to have engaging characters. Games like Fire Emblem: Awakening can compensate for its lack of strong central narrative with interesting and well-written character development.