I don't mind a slow burn, personally, though I do want there to be at least some exciting situations and a promise of more to come. If an adult game sticks to "we're just in a friendly/professional relationship" for too long it does get boring. But a slow burn can make the eventual payoff all the more exciting.
I feel the same way about transformations - a one-time transformation near the start of a game doesn't add much for me because you might as well have started out like that, but a slow transformation or a transformation with multiple stages can be a lot more exciting.
Mind you, I do think "the bigger the better" - I just don't mind if it takes a bunch of time (and a bunch of stretching) to get there