^Id agree with that, apart from Echoes where the keys were just plain annoying. I think Corruption was the worst in the series, even though it was still really good.
Didnt have the atmosphere of the others and felt no-where near as epic. Partly because there was very little exploration and that the bosses had the exact same arena each time.
There was a lot that was added to corruption that hindered it, such as adding the other hunters.
Samus is better off as a solo artist not a crappy band.