What I want to see in the new cartoon:
Have the current voice cast, because why not? They are already voicing the characters, so why not let them voice the characters in this show? And I think that they are pretty good voice actors for these characters.
Have the tone of the show have a nice balance between being humorous and serious. It doesn't have to be one or the other. I always think that the Sonic the Hedgehog franchise works best when they are balancing the humor with the serious moments. The last Sonic the Hedgehog cartoon I've seen that had a nice balance between humor and drama was Sonic X and I'm hoping we see that type of tone for the new series.
Develop the characters and the plot very well. One of the biggest issues going on with the video games as of late is that the plots and the characters are poorly written and I wish that they try to write these characters and the stories a bit better. I'm hoping that the cartoon series would be well written like the IDW comics so that way we would have characters who are well liked and interesting to watch.
Don't have SEGA be too involved with this series. Now, if SEGA were doing a good job with the games at this moment, then I probably wouldn't mind SEGA being heavily involved in this series. But, because lately SEGA hasn't been doing a good job with the characters and the stories and because their mandates for the characters are a bit ridiculous (having Shadow acting dark and edgy without any character development or not clearly explaining about why only Sonic, Shadow and Silver can go super), I would rather have this series be its own thing and try out plot lines and character interactions that you don't see in the games.
Finally, hire some really good writers for this series. I've mentioned that good writing is the key to having a successful TV series and if this show has lots of good writers on board who know the characters well, then I can see this show being successful. Some writers I would like to see on this show (if they ever get the chance to write this series) is Ian Flynn, who wrote the comics for years.