The original is a decent kids' show. Nothing more, nothing less. I remember it being pretty pure.
The original follow-ups, ultimate alien and alien force are kind of edgy continuations that attempt to grow up with the original audiences. I found it fascinating to watch a children's cartoon show where the straight up US military showed up to intervene in the protag's business, but it wasn't really... That good.
Omniverse is polarizing on here. It's still a continuation of UAF, but with a much more lighthearted tone and stylized artstyle. Not like teen titans go or anything, though. More like the original Teen Titans- which makes sense, considering one of the guys that worked on that worked on this.