I've had lots of fun with the game, but my gripes against it have piled up lately.
Spirits/World of Light - WoL and its counterpart were a welcome sight after the lack of Subspace in Smash 4, and it was actually a really fun mode to fool around on and learn the beginnings of the game if you were new. The main problems in the mode were pretty straightforward. WoL has no replayability once you've completed it and is a chore to get through the first time. WoD, on the other hand, feels rushed, as if it was a last minute addition because the first map was considered "too short".
Spirits in general are a lackluster replacement for trophies and to an extent, stickers. Most are .pngs of existing assets in games and such, with very few being original remakes or designs. They don't hold any real value as was advertised, and combining valuable spirits just really doesn't feel impactful in a way as they might have intended. Trophies had mostly the same thing, but gave you history about the characters, or fun little quips about who they were and what they did. Zooming out on your trophy collection after scoring them all was a feeling of real accomplishment.
Eco Fighters - When I first saw the information about Echo Fighters, I was actually very excited. They were actually making the clone system an actual thing and every echo fighter would be its own thing based on the moveset of an original fighter. My hopes for Daisy/Dark Samus/Richter were pretty large.
Fast forward to release and I'm disappointed. Each play the same as their counterparts with VERY minor differences (Richter's side B has aura properties from Simon's as an example). The only one I could say is different would be Chrom, but that's only on the fact his kit combines 3 other FE character's kits into one. Remember back in Melee when the differences between characters with similar kits were noteworthy? Luigi had a similar moveset to Mario but was different enough for him to be a separate character? Luigi's nair sent your opponent up instead of away, his down B hit twice instead of multiple, instead of a cape, he had his own side B?
Online - Everything's been said to death so this will be short. Why do I have to play on somebody else's ruleset half the time? If I don't want to play matches with items or smash balls, then I don't want to play with them, period. Why am I at the mercy of another person's internet when the match starts lagging? Why is GSP so meaningless in this game?
"New Tech" - My main annoyance with Nintendo is that if a new tech or strategy comes out, it's immediately removed or nerfed so far into uselessness that it's worthless. This is why we don't hear or see so many "new tech discovered" news or information as before. They seem to want us to play the game "as they intended it" which is no way for an online fighting game to be handled. I'm not expecting techs on the level of Ice Climbers wobbling or desync, but at least something.