I love Dragon Slayer and the speed of the battles along with many of the hits are very satisfying. Optional animations and misc effects would be nice, but they didn't look great in most JRPGs that generation and quickly became a pain to sit through.
I also love the enemy designs, color and pixelart. Again, too many games have boring and unoriginal enemies. When you have a solid style, it doesn't matter if your game features lots of stereotypical creatures.
The optional custom leveling system is also really nice and would be considered revolutionary in a SNES game with a SYSTEM title.
I did not like DSII though.