Just seems a little bit lazy to use the same six characters for the main cast again desu. I don't have anything specifically against the design, I just think it might have been wiser to try to actually start fresh if their intention is to actually start fresh.
It's an exceptionally transparent example of people prioritizing advertising and branding over storytelling. The only way I can see they could subvert that is if they made the plot somehow revolve around how the characters have changed and how their dynamics are different, but frankly I don't see them doing that.
I'm not saying G5 is going to be bad, but looking at it from an artistic integrity standpoint it can be said that they should have made new characters instead of reworking old ones unless there was a very good reason for reworking them and I doubt there will be an adequate one. As such the decision to simply stick with the same characters, again from an artistic integrity standpoint if nothing else, is somewhat contemptible.
Maybe they'll have a very good reason for it and G5 will be better than G4 in the same way that G4 was better than G3. I hope that's the case, but I'm certianly not going to hold my breath.