I didn't follow the development very closely, so I can't speak to whether they overpromised.
I am playing through Reforged's campaign though and it is the same top notch game with better graphics and a few other minor improvements. Which is sort of what I felt I was promised?
My views on this have evolved.
I was close to the end of the Warcraft 3 campaign (so, had not started Frozen Throne), when it truly started to sink in just how little they had changed/improved. There is a map in the human campaign that is largely reversed because its layout is different in World of Warcraft (never played WoW, had just read about it). It was SO much fun. They didn't do anything too it except change the layout a bit and it was a massive improvement and new experience. It puts in contrast just how little value the remaster adds.
I hadn't even begun the multiplayer with all the issues people were reporting.
So, instead of playing on, I got a refund. When I did that, I immediately lost access to the game, to discover that my copy of Warcraft 3 classic had had its progress over-ridden - I need to replay the campaign. I did start that, and it took me a while to realise the graphics were old, so minimal are the improvements.
I think gamers need to take a share of blame as well. Reading more about the development now, at multiple points we demanded "make it new, give us more, but don't change anything." We stupidly protested the idea they wouldn't use the original voices, that they might change story elements, that balance might be addressed. I can't fully blame Blizzard for being too nervous to change anything. I can blame them for charging $45AUD for changing nothing.
starcraft - Playing Games = FUN, Talking about Games = SERIOUS