A part of me would like a return to more consistent power-ups as opposed to the timing based ones, but one advantage of the timed powers is that, when it only appears at very specific points, the level can be designed to utilise it to a greater extent. If the player is allowed to take their power-ups into every level, they have to be slightly more generic, because you have to be able to complete the level as regular Mario.
I suppose it's okay to have little secrets in levels that can only be found by using powers. But you couldn't have a level where you NEED to use the Raccoon Suit to finish it, as you might arrive there without it, and then you'd to have to back out to find it elsewhere. Not really a good idea.