Rocko's definitely the best show as an adult - it's legitimately funnier than most sitcoms airing today! Aside from that... I'd imagine early SpongeBob, Doug and Hey Arnold still have some entertainment value, but I'm not sure if I'd revisit anything else. The Klasky-Csupo stuff is definitely more kid-oriented than family-oriented (except maybe The Wild Thornberrys), I never really liked Ren & Stimpy or Zim, and truthfully, I remember The Angry Beavers not holding up very well when I tried to rewatch it.
In general, I think Cartoon Cartoons held up better. Johnny Bravo, Dexter's Lab and Sheep in the Big City seem even funnier to me nowadays! I think CN's shows tried harder to appeal to all ages, whereas I think many of Nick's shows were kid-only ordeals.
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Unlimited juice?
This party's gonna be off the hook!