Technically it makes more sense than how disguises have been handled in BM (and older Hitmans) traditionally - a strange bald dude suddenly appears wearing your friends clothes (who has now vanished) - the guards are understandably a bit miffed, until you consider disguises which feature a mask of some sort still arouse suspicion within 1.5 seconds (at least on expert mode). You pretty much don the disguise, check the coast is clear then move from cover to cover trying to avoid the enemy line of sight. It is more unforgiving than previous games and combined with the new cover-based line of sight for enemies and smaller levels has a net effect of occasionally making you feel rail-roaded through some levels in a particular fashion, essentially restricting how far you can go off the beaten path so to speak (though this is dependant on the individual level setup). I expect a purist run would be an absolute b**** since some sections rely on instinct stealth + disguise to cross open areas with little cover and many enemies. Overall, its... different and you can see the influences from other games that are eroding the traditional Hitman approach, but that was (for me) to be expected somewhat due to the large gap between BM and this.
As a side note, enemies are all now highly susceptible to audible distractions of your own making, its a fairly painless process to empty a room of enemies by throwing an object to lure them out one by one, typically only one guy will come to check it out.
This comment overall summarises my feelings as well. It feels like most of the systems are there in the game but it just doesn't pull it off in a cohesive manner, very much a Codename 47 situation. The potential is there to bring back the missing elements from the older titles and integrate them into the new framework, though I highly doubt this will happen as the industry leans towards continuous streamlining nowadays. It could have been a lot worse, but the disappointment isn't lost on me either. Despite all that I am enjoying the game so far (just hit the Saints section of the game), decent length too.