Abandoned is the perfect word I would use for how I felt at the time New Adventures came out. And yes, Mattel failed to realize the passion we had for the original characters. It essentially begged us to forget everything we bought into (literally and figuratively) during our childhood with Masters of the Universe. It was a betrayal, at least for 7 year old me at the time.
Honestly, I think NA in itself, is not a bad cartoon. I think the problem is that it's associated as a He-Man/Skeletor cartoon. I look back, and wonder why the original He-Man and Skeletor needed to be in it. Why couldn't Mattel have just made a new fantasy line? Essentially, they did make a new fantasy line (in space), and attached the He-Man and Skeletor names to the hero and villain. I'm not sure if anything could have overthrown the TMNT express in that time period, but I think New Adventures would have gotten more respect if the toyline and cartoon had a main hero and villain with their own names and background. I bet I would have given it more of a shot, rather than feeling my favorite characters were abandoned.
Now, I apologize if my reply sounds harsh in anyway. You know how thankful I am to see your contributions here. What I just want to get at is this - I think both New Adventures and the original Masters of the Universe fans were disserviced by being lumped together as the same thing. New Adventures wasn't Masters of the Universe. It had its own adventure and style, and deserved its own beginning. Creatively, I feel like too many things are just used over and over again living off another name. I don't know how much we have to continually re-invent things. I guess there is a safety net in that, both in the minds of fans and companies.
If Masters of the Universe taught us anything, is that new stuff is exciting, and allow for a lot more creativity. New Adventures deserved that same opportunity.