The cartoon was one of the best cartoons ever, and it gets reruns regularly here in Brazil (being the cartoon most-clamored-for by the viewers).
No demons? What about Venger, or that half-demon chick in the "Son of the Stargazer" episode, or the clock-keeper in "The town at the edge of midnight"?
As far as cartoons went, Uni was far less annoying than similar "pets" (HERBIE, anyone?), and even served a purpose in several episodes (like the one with the Black Unicorn).
The plots constantly misled the audience (the Merlin, Skeletal Warrior or Shambling Mound episodes) and surprised every now and then. Plus the settings were amazing (Venger's prison built on top of a volcano? Very cool!)
So what the weapons never killed? G.I. Joe was far worse in that regard. Plus we got to see the remnants of dead soldiers (the Labiryth), undead (zombies!!! where can you get zombies in a kid show?) and falled heroes (the Hall of Bones). We also had the heroes consciously decide NOT to kill the main villain (the Dragon Graveyard).
The D&D cartoon was my first experience with D&D (I only started playing a couple of years later) and it was very, very good.