Shining Force was created by a guy who really didn't like Fire Emblem, and it shows. I don't really consider this a bad thing, since the original FE1 was not great.
So, my experiences as follows: SF1 didn't so much have a difficulty curve as a difficulty valley. the beginning was okay, then it got really easy once you promoted up and started getting insane stat boosts, and then it got hard again once so many enemies just plain ignored defense. The magic adjustment in the GBA version did the game no favors, but Narsha is pretty cool, so no probs there.
SF2... I really want to say that this game is great, but there are so many characters not worth taking, and so many characters and decisions that are complete no-brainers (most of the alternate promotions), that it wasn't really able to realize the potential that it obviously had. Still played the hell out of it, though.
Also, while the console ports may be rough stuff, the PC ports through Steam run perfectly.