My feedback considers 6v6 only:
-Spectator mode.
-No automatic animations where players get stuck into animation.
-Reward goalies more for good positioning, punish them more for bad positioning.
-Fix the goalie movement in the butterfly stance. After that goalies should be required to stand up while the puck is far away from the net and stay in the butterfly stance when the puck is nearby.
-Consider forcing goalies to react to shots by going into butterfly, if it's possible with the latency of online gaming. Especially in early stages of the NHL 19 goalies shut the five hole way faster with automatic save animations than by hitting R2, which made using R2 completely pointless as you got beat more while trying to react to the shot rather than just letting the game handle the save by itself.
-Keep the deflections somewhat as they are: force goalie to challenge the shot to make saves on high percentage, punish them hard for sitting inside the net when the shot is coming from far out.
-Deflections should be possible only for players who are either standing still of very slowly gliding by. Right now it's ridiculous how skaters can move 100 mp/h and still make deflections. The slower the player moves the higher the chance of deflecting the puck should be. Maybe even making deflections manual would be a good choice.
-Remove the auto covers and sweeps from the goalie once and for all, only the certain covers and sweeps should be automatic (just like the ones that are automatic nowadays). Autocovers were ridiculous for half a year when goalies intercepted passes with covers etc. Goalies are also playing the game, not flying on an autopilot.
-Stick lift and stick checking should be more balanced and require the defensive player to actually be able to reach the stick or puck. Stick lifts should be effective but lifting the stick through the body of an opponent shouldn't be possible.
-Pucks should move towards the direction players aims to, not the direction games decides it to go. Right now there are tons of shots that are, for example, aimed to top left corner but go through the five hole of the goalie. Also shooting the puck wide should happen more when the player isn't facing the net in a proper way, and happen less when the player is.
Just to show something related to the movement of the goalies. Check out the video below and imagine if Jonathan Quick had to move the same way goalies on the NHL 19 do: moving around in the butterfly stance, having to move at least 1/3 of the width of the net at a time, as it's not possible to move less. Also the real goalies' movement from the stand-up to butterfly and back up is extremely fluent and fast.
Few timestamps you might want to check out: 2.43, 3.45, 6.07
Edit: I also have to note the game shouldn't try to be too realistic or too close to real hockey, as it may not be the best possible thing for a competitive e-sports game. I'm just trying to note that the movement of the goalies could be way smoother and transitions more fluent than what they are now - but then the requirements for the goalies to make saves should also be higher (positioning wise etc).