Not gonna lie, I am somewhat disappointed by the lack of voice acting. Part of the fun for me was going to be hearing all of these Nicktoon characters interact with each other. Having Nigel say "SMASHING", or Danny Phantom say he's "Going Ghost", or SpongeBob tell Lincoln Loud to "Bring it around town", or basically anything from Zim and Michelangelo would have really tickled my eardrums. However, I feel that they could use this opportunity to make the core fighting gameplay and modes for the game much more polished. Plus, I would rather them implement voice acting smoothly rather than unsmoothly.
Take Cartoon Network Punch Time Explosion for example. That game did have a certain amount of voice acting. However (and correct me if I'm wrong here, I haven't played the game in years), many of the characters did not say much of anything to each other while they were fighting. No grunts when they got hit, no sayings when they used their special moves. The only time you really hear them speak was when they either got knocked off the screen, or won the match. And even then it was only one line of dialogue each, or the narrator said something instead.
The story mode had this weird thing where the characters both spoke through voice lines and text boxes, but the spoken dialogue really only seemed to serve the purpose of telling the audience who was currently speaking. Idk hearing Flapjack say "Hi friend!" while having the dialogue box say something else entirely was really jarring and honestly took me out of it. Coupled with the fact that the pictures next to the text boxes already showed which character was currently talking, the voice lines at that point seemed really unnecessary.