Just had my first playthrough with kelvin and had some difficulty with the experience:
could not tell if sublimate was doing damage/stunning foes (game indicators are turned on). Ice wall did not seem to be blocking/stunning foes most of the time. Could not tell major difference, at first, between primary/secondary attacks. Could not tell visually if Chomp landed successfully.
The biggest playability issue so far is specific to Isic Magnus - could not tell if I was landing hits on the leg canisters at all, spent a majority of the mission in melee range BUT stuck in the Magnus model (especially when exiting Sublimate form) and the last combat stage (Flying DigiSkull) I could do nothing to contribute.