id say 9.8. Game is great but I only have minor grips with the game.
Casually there is nothing wrong with it that I can think of.
Competitively, Many defensive oriented options have alot of viability overall, which can lead to people forcing defensive games and help encourage defense oriented play. This is bad as it greatly slows down the pace of the combat and can lead to boring styles of play, as well as excessively long games. In a fighting game Offensive options should ALWAYS be overall greater than defensive options to encourage more engagements and styles of play. I don't think defensive options shouldn't exist, just that they should be noticeably weaker than they are in sm4sh.
Second issue is with diddy and any other easy to use top tier characters. I was fine with sheik and ZSS being potential top tier, as both took a fair amount of skill to use effectively, Diddy doesn't, Its the same issue with metaknight in brawl, though not to as severe of a extent, Hopefully the meta developed enough that Diddy becomes easily countered, but for now its a problem. In short easy to use characters should never make it to top tier, hard to use characters should make top tier much more often, with the exception of under powered 'challenge' characters. Yes distinctly under-powered characters serve a purpose in the games design, and overall benefit it. This wasn't a issue in melee or PM as the top tier characters took alot of skill to use effectively, and that skill was needed at high levels up play, in Brawl with MK, and to a lesser extent, Diddy in Sm4sh, neither take as much skill as most if not all of the other high tier characters.
I do not find issues with things like how long it takes to kill a stock in this game. The game and engagements are overall similar to past games with the main difference being more time in the neutral game and more engagements need to be won to effectively take a stock. All you should need to do is drop the number of stocks needed.