I'm liking it - haven't played very much of it yet, but had a look around the first mission.
It feels much smoother than the beta. You can lock the framerate at 30, or leave it unlocked. I prefer how it looks unlocked - much more fluid - so have done that. There is a small amount of slow down, but nothing very noticeable.
It really does feel like a sandbox - you can tell there are so many ways you could accomplish the task. It doesn't feel force-fed. like the previous game did - much more open.
The mansion is extremely impressive - a lot of people on screen - the fashion show is very well done.
Looking forward to putting some time in - looks and feels like a Hitman game should do.
One negative is that for the full experience you need to be online (for challenges etc). Unfortunately, it keeps dropping the connection (not my internet, but to their servers). When this happens - you get thrown back to the main menu screen and lose your progress from the last auto save point (these are very frequent saves). Very annoying, so I played the mission offline - which is less annoying as you don't get kicked out, but will be good once they fix their servers.
Also, the loading times are very long - abut a minute to load up a saved game. Given that these games are about experimentation and trial and error, it sucks that it takes that long to load up a game if you want to go back a step.
But recommend it if you liked the earlier Hitman games.