Though it hasn't opened, I would lay odds that Slink Dog coaster will be the most overrated. For me, SDMT is fun but I only waited on it as standby when it was a 30-40 minute wait (right after a shutdown/restart). Way too short. Feels like it no sooner got rolling and then it stops. The actual coaster sections don't have enough length to feel like a ride. Plus, it takes up prime real estate. Though WDW has all that land, the parks are actually small and not well laid out. SDMT is a good example. It is landlocked and value engineered to eliminate what could have been a truly awesome coaster.
For what it's worth, my wife always asks me why they had to get rid of Snow White's Scary Adventures and I don't have a good answer. That was an okay ride, not awesome, but enjoyable. I think that both rides could have coexisted easily enough.