I am not sure if it is worth to share my first impressions now that this camera is two and a half years on the market already. But maybe it is of interest anyways. The X-Pro3 is my first X-System ILC, the positive experience from my X100V purchase let to an expensive and unwanted GAS attack, which resulted in the X-Pro3 and a trio of primes a few months after I got the fixed lens compact.
To be honest there aren't many negative things I could talk about. The camera doesn't feature IBIS, coming from Olympus that's kind of a bummer, but to my own surprise and don't miss IBIS too much - something I already noticed prior with my X100 - as I simply accept it when I pack the camera. I prefer the ISO-dial design of the X100V, which doesn't need to be held up while changing the ISO but instead needs to be clicked down into place. A disappointment are actually the strap lugs: It seems to be a Fujifilm thing to only install tiny lugs on their cameras, I might've understood that on the small X100 models, but not on the big X-Pro. My Sailor Strap neck strap, which easily fits my small Pen-F, the bigger E-M1 and seemingly a bunch of Leica rangefinders is a pain in the a** to attach to the X-Pro3. Even when going through the hassle it barely moves at all. But that's about it, on to the good things.
The camera feels and handles great, the buttons and dials are firm, clicky and tactile, a positive surprise from the X100V, which in my opinion had rather mushy buttons. The ergonomics are great, the added thumbrest on the rear and partly the molded grip on the front is a big plus compared to the compact sibling. For me it's mostly due to the thumbrest on the rear, something I already loved on my Olympus Pen-F. The Q-Menu button is in a better position and I like the additional function button which is right above it.
I generally enjoy the rear screen of the camera, it can be quickly folded down to allow simple waist or ground level shooting - the only downside when compared to the Pen-F's fully articulated screen: Shooting at ground level in portrait orientation is essentially impossible. The gimmicky "film" display is in my opinion a neat little touch, both for information as well as asthetics.
The hybrid viewfinder, just like on the X100V, is in my opinion great and one of the main reasons why I bought the camera after all. While I do use the EVF at least 90% of the time, there are situations where I either really like having the OVF or use it as a challange for fun. The EVF seems to be most usefull in the ~18-60mm range. My 16mm is already quite a bit wider than the OVF, while my 90mm is already fairly challanging due to the small frametimes - it can be done, but not as good as the 50mm and I wouldn't want to go any longer than 90mm.
Bottom line: The X-Pro3 is pretty much everything I expected - a fun to shoot camera, which feels and handles great. I applaud and appreciate Fujifilm for trying something fairly different with the X-Pro line and particularly with the XP3. The camera is different in a good way and I hope Fujifilm is going to keep the line alive in the future.