I used to hate the Snake Men. When I first got all three of them as a present, I read the mini-comic and said "***"? They just didn't seem so threatening back then, since their numbers were so low. Actually, they seemed like generic Lizardmen.
They originally were just more Evil Warriors and all had corny powers...King Hiss was basically a pile of snakes, Rattlor and Tung Lashor seemed really ridiculous in She-Ra's cartoon. The Snakes collectively not being featured in any television media didn't help (I'm guessing this might be the same for the other 1986-88 characters who never made it to Filmation's cartoon). I'd guess not featuring the Snakes as a group in any Filmation cartoon might have given the Snakes a "I'm not getting them since they were never in the cartoon factor" that many fans might have decided on.
Maybe the fans who always thought that the Snake Men were garbage were unprepared for seeing such "worthless characters" suddenly become overnight badasses in 200X? Hordak was always portrayed as the ultimate villain from jump because he was Skeletor's teacher and even Skeletor feared him, adding to Hordak's rep as being far worse. Originally, King Hiss and two other dudes were so much of a non-factor, the Snake Men had to immediately team-up with Skeletor. Even worse, Hiss needed one of Skeletor's men to give this new faction some weight. It's akin with teaming up with Skeletor because you have nowhere else to go...
200X changed my attitude toward them as now, not only were they not some more throwaway dorks working for Skeletor, but they were an actual threat, making some of the laughable abilities more threatening. I can understand why they would be pretty powerful, as there are only six of them (God forbid Mattel made any more Snake Men as toys; the fans would have a fit!), but they did go a bit overboard at times (regeneration in the dark, underwater modes, etc.) it was like, "what couldn't the Snake Men do"?
But now, I could see how the 200X Snake Men were such terrors. Not only did he turn everyone the Snake Men encountered into Snake Men (adding to their legions), the Snake Men were additionally very powerful.
As for the Snake Face issue, his "Medusa gaze" was too powerful. He could sideline a character permanently very easily. Not even He-Man himself could do this. Maybe in time, it would have been changed somehow to a temporary ability.
On the Snake Men having a whole season to runamuck: I think it's only fair, seeing as though the Horde would have been doing the same thing if there was a Season Three.