Nice man. Contracts will be a treat, especially since you haven't played C47. The Hong Kong remakes drag the experience down for me because -- unlike the Rotterdam remakes which are completely re-imagined and the Traditions of the Trade remake which is a level so good that having a second version is totally cool -- they just seem like retreads that don't add much new or interesting, and there's 4 of them in a row. But you won't have that problem since you haven't played C47!
The change in tone from SA to Contracts really is an impressive feat. It's too bad that BM couldn't capture as strong a unique tone as SA and Contracts did, because BM really did imo perfect the sandbox level design and is therefore the most replayable.