Cultist is underrated, probably from lack of experience at the time we voted. And Hunting Party is overrated, which I think is consistent with the general trend that stuff that is simple is viewed as being stronger since it doesn't require too much thought or skill to play it well enough.
IGG is overrated.
Where do you have it?
The way I see it, it's bad when there is strong trashing, but otherwise it's like completely dominant. That's worse than the junking attacks and Wharf and Governor and Rebuild, which seem to be key cards practically all the time, but it's better than everything else.
I don't think it is overrated. There are few strategies that can beat uncontested HP. And contesting and losing 6-4 is normally gg. Even cursers have decent counters (trashing, sifting, HP), and losing the curse split 6-4 is alright if you have slightly better economy afterward.
I'd say for the $5's there is a big 7: Wharf, HP, Rebuild, Cultist, IGG, Witch, Mountebank. The order within these depends a lot on individual player preference -- ie. BM vs. Engine.
Then it's the group of MUCH more board dependent cards: Torturer, Minion, Governor, and (not as much so) Ghost Ship. Torturer needs village support, Minion needs trashing, Governor needs one of a number of things, Ghost Ship isn't as much so.
But, those are just my thoughts.