I'm quite liking Pro mode so far, though I've only successfully completed so far 1 run each of Paris, Sapienza and Marrakesh.
To me Pro mode is basically a "New Game +" mode, and in that regard I think it's overall a success.
I like the camera and footstep detection changes, the limitation on saves, the way you really do have to rethink approaches and how it's all made somewhat fresh again. I also like, as @RW_Slick mentioned, how it's more important than ever to plan out what you want to do and be strategic about your equipment slots, and how -- for me at least (because I don't yet know all the ways in which these once familiar levels have been remixed) -- even with that careful planning, you may need to improvise and revise your plan half way through, finding ways to use the equipment you brought that may not be how you originally thought you'd use them.
There's a tension and feeling of greater stakes in Pro mode that is very reminiscent of the classic Hitman games and which I didn't fully realize until now was missing from HITMAN in its standard incarnation.
But I do think there's some missteps. I'd like there to be a slower attention gain on suspicious items than on illegal items. Remote detonators should not be detected by frisk - that definitely seems like an unintended result. When disguised as a waiter/kitchen staff you should still be able to hold kitchen knives (but not combat knives, of course). I haven't tested this yet but when disguised as a mechanic/crew member/handyman you should be able to hold hammers, wrenches, screwdrivers.
I also think there's a bit too much of "item now being carried by random NPC" going on. In some cases (like safe combination codes) I like it, it's logical, it makes sense. But I don't like how you have to rely on knowledge from previous runs or the internet to know that, e.g., random dude X is the guy with the rat poison. I'm overall good with the drastic reduction of items just laying about, but I think they may have gone slightly overboard with this and I wish the items tucked away in people's pants were put back into real-world-logical places. Or only put in the pants of real-world-logical people (i.e., screwdriver on the guy you SEE working on a lighting rig with a screwdriver animation, that sort of thing).
And that's what I think. Overall I'm glad it's here, I'm enjoying it quite a bit and it is, for me, giving a "New Game +" -like second life to the game.