Odin Sphere is technically a sequel to a game never released in the states known as Princess Crown, so I am going to list Odin Sphere.
In some respects, I think Xenosaga Episode II did Xenosaga Episode I a lot of favors, while completely removing good points from the first game. Xenosaga II was fun and all, but it lacked a certain something the first one had. But hey, at least the battle system was better, the overall graphics improved, and the sound design in terms of music is somewhat more memorable than the first, even though they're pretty much on par with each other. I wish the story and voice acting received the same treatments.
Also, Saga Frontier II did the original a lot of favors by keeping it more linear and focused, as well making the overall feel of the game less cheap and forced you to rely on strategy and not just spamming the same JP, WP, MP attacks over and over again. If you found the right move in the original, you could spam it over and over and win in a flash. Not in Saga Frontier II. Oh no...This time, you were pressured to be more diverse with your tactics. I found myself increasing stats just as often as I used spells, melee attacks and healing, because the enemies were well balanced, at least from what I have played of it, and by that, I mean half of it. The sprites were also cleaner and more defined, and the spell effects were better, but the story...Not so much. I didn't understand it, but I kept playing because it was challenging. I was actually WAITING for boss fights and looking forward to losing in some instances.
Also, BlazBlue Continuum Shift included a lot of features that should have been in the first game. If BlazBlue Calamity Trigger had just come with challenge mode, and the same robust features in training mode, it would have revolutionized 2D fighters for all they're worth. EVERYONE would have been copying the formula and frankly, the game would have been more fun, had it just included tutorial and challenge mode.
Also Bleach: Dark Souls, despite being a Bleach fighting game, was really, really fun. For months on end, I would have that DS card in my card slot, because I wanted to unlock every character, get every gem, get every card, and master every character, which I found to be quite enjoyable actually. My favorite characters were the Captain General (his name escapes me at the moment), Kyoraku Shinsui, Ichigo Kurosaki, Soi Fon, Kisuke Urahara, Toshiro Hitsugaya, and Momo Hinamori, mainly for their play-styles. Each one had a unique mix of melee and projectile attacks and it made the experience much more fun. Soi Fon was easily my favorite out of all of those however, because of her speed and Level 3 super attack when landed twice. Instant KO'ing the opponent was AWESOME.