I like Echoes. I just am not exactly fond of the exact choices they made regarding them.
Lucina was great in Smash 4 as a newcomer, still is. The moveset and playstyle of Marth is so much based around timing, precision and being in the right position all the time, even one little change is significant to trade that around. Lucina was a great choice to add, as she's a very important character in Fire Emblem, and they seemed to have learned about the mistake in Melee with Roy. Chrom is much the same, expect his changes from Roy actually make him better.
I also would've liked if Samus was more powerd based than Dark Samus, who could be a bit more technical, have more multi hitting combos, just anything. A awesome thing that would be canon as well is having Charge Shot with less power, but having a sort of poison or Phazon property on the move, that it adds a little damage over time. Another change I'd add to Samus herself is basing her of the Samus Returns redesign, and give her chargable Missiles. Dark Samus then, would be much like Young Link, based around the more classic version of the character but added speed (Dark Samus shouldn't be that significantly faster however).
Chrom also shouldn't run as fast as Roy, in fact he should be just a little faster than Ike to justify his power. This also gives Roy his unique artibutes that work in his favor, as he doesn't have the range as Chrom or the other Fire Emblem Lords do. Flare Blade also could've been a projectile, or be more ranged.
Dark Pit is a funny one. They got the Staff from Kid Icarus Uprising as a item, but they didn't give it to Dark Pit. That would be my one change probably. Though I kinda have a hard time deciding which Special attack I'd change for it. Dark Pit and Pit being so similar kinda fits anyway. That's why the character has grown on me a lot, since playing Uprising.
Not sure what to do with Daisy honestly. As Daisy never did much in canon. Maybe make that Football item her Down Special instead of the turpins? That would make her be based more around the Mario Sports games? Her having Toad also feels weird.
With these small adjustments, the characters would be much in the same position as Pichu. Dr.Mario and Young Link.
I like the Echoes, but ever since Ken's reveal, I always thought what they did with the other Echoes is wasted potential.
I also still really want Impa as a Echo to Sheik. Am kinda salty that I don't have this option.