Sonic is not supposed to be Mario

It's understandable Sonic dropped its "cool" act since mascots built on the concept of being "cool" and "rad" died in the 90's (I miss you Gex). What you're asking for is maturity which is not the same thing. Sonic was not built on the concept of being "mature" and when it does try growing up, you get abortions like Sonic '06's story or Shadow The Hedgehog (both the character and the game).

With the latest title (Sonic Forces) getting laughed out the door for its try-hard edginess, I hope SEGA realises that Sonic is not for a mature audience (not saying you can't like it but the target demographic is children) and never will be.

If they want to broaden their horizons into the 15+ crowd, bring back Vectorman, Streets of Rage, Golden Axe, Bonanza Bros., etc. those games aren't exactly family-friendly and people WILL pay for a sequel.