Just because it's adult animation doesn't mean it's target audience is people in their 20's, the target is Elvis fans. I'm 35 and have been a fan of Elvis' for 22 years. I'm under 40 and I don't need to reference Wikipedia to know who Dean Martin is, unlike one user review suggested. I was born in '88 and had listened to every available recording of the Martin & Lewis radio show before I was even 20. When I watch Agent Elvis and delight in the references made about the other greats of the time, I feel like the show was made specifically for me. If a show can make a viewer feel seen, then it's a good show in my opinion.
This show pokes fun at everything Col Parker wanted Elvis to be, making light of the failed attempt at a Christmas special, the terrible movies, etc. I feel like Elvis himself would get a kick out of this show, especially with it not being G or PG rated. We all know Parker would have brokered some kind of deal with someone to make it a family friendly production and sucked the joy out of it in the process. Thankfully we have Priscilla at the helm, and considering her involvement in the Naked Gun movies, I don't doubt her judgement or sense of humour.
I don't think this show was made to revolutionise adult animation, I really think it's just a treat for Elvis fans. Everything the Presley family has done since Elvis' death has been to keep his memory alive, and having something new like this, instead of re-watching everything else he's done for the millionth time, is a refreshing way to remember and enjoy Elvis Presley.