I have 60 hours on the game, and I find screwing around is just as fun as it was in 2, though the warden fights got really dull quickly.
Well, I managed to pull 100 hours on SRTT with mucking about and going with a zombie voiced replay (sort of sad it wasn't in SRIV), but as I said: I'm used to really MASSIVE content that basicly means I can muck about in so many different ways that it's actually rare for me to ever finish the main story line because there is just so much other stuff to do. And in that department SRIV is lacking, there's really only one thing to muck about with and that does get stale, especially if there is zero character interaction. There's nothing left to explore, and save for one you can't pretend there are any secrets in the game to find either.