So, I finished this a few weeks ago and I must say that I quite enjoyed the game's expansive levels. They are well designed and quite varied, and definitely pose a challenge. I also like that IO is continually supporting the game with the use of elusive targets, and escalation side missions to give the game considerable longevity (since, to date, there are really only 6 levels (plus the prologue). There are a few "bonus" missions that have been released and they were quite fun as well.
I've heard that in conjunction with the release of the retail version of the game at the end of this month, they will be releasing an update that will introduce a "Professional" difficulty level that will "enhance" AI, restrict items, restrict disguises (i.e., supposedly, if you kill a target with a pistol to the chest, the disguise won't work), etc. The only problem is that apparently the difficulty level requires Mastery Level 20 for a particular level in order for it to unlock, which requires a lot of play time. In all likelihood, I will never unlock Professional difficulty level since I have very limited time to spend playing games nowadays. But some exciting stuff for die hard Hitman fans.