Ziggler was a hot commodity just a few months ago. He was being talked about positively on here. I think we, as fans, are incredibly fickle. He's been in some lackluster storylines ever since Survivor Series. A potential great feud with Bryan never really came to fruition. They had a couple matches, and that's it. It never really evolved into anything. He was white hot all throughout the Survivor Series storyline, defending the IC title. He showed what he could do, and the sad truth is that spot wasn't even meant for him.
No, I don't think Ziggler is overrated. I think he is under-appreciated. Booking has damaged the perception of him lately. This Rusev is feud is silly, and Rusev is coming across as the babyface. If he's given the ball, he'll run with it, and I think people will look at him differently again.
As for Neville, how is he overrated, exactly? Most people know he's good in the ring but lacks mic skills. He can't carry a feud whatsoever. What he does do is garnish a feud. He can put people over. Of course, he's not treated like a big deal on the main roster so that dampers it, but because of his in-ring capabilities, he can turn a great feud into a memorable one because of the match. So I think he's a valuable talent. But he'll never be "the guy." I see him in the upper midcard, which isn't a bad thing.
I don't think Ziggler is held in as high regard as he was a couple years ago by fans anymore. He used to be pretty overrated but most people don't really seem to care about him anymore. He's decent in the ring, decent on the mic but he's nothing special. Just a mid carder for life.