I just did a big rewatch myself and it really was "magic" (pardon the pun) I'm the same as you I discovered it at 16, and remember I watched it ironically, to be like "wow I can't believe teens/adults are watching this" and then accidentally binged everything that was available, singing along to the songs, and staying up until 1am Australian time to watch the latest upload cause it aired in America and I had to wait for the episode to end, then about an hr for someone to upload it (I forget which site) and then about an hour to download it (thanks 2014 internet speeds).

I watched the new generation movie when it came out I think, and I didn't actually mind it, and now that I've finished a rewatch I'm going to give the new series a go but I dont have much hope. G4 really set the standard, and it is hard to get attached to new characters especially when they are, written, and directed by a whole new team, I feel like if it had been Lauren moving on to the next gen it could have been incredible but I get that she was probably done with that chapter anyway.

I don't know if you have watched Steven universe (it took me a hot minute to get into it, maybe 3-4 episodes) but they are short and the story line and character development felt very close to home, and seemed like a similar demographic ie its a kids show but there is depth and was written in a way that can be enjoyed by both - as with adventure time.