Looks professional and a little bit overwhelming in possibilities! That is good and complicated! 
Although I tried older versions of RT in the past, the 5.3 release looks like a more mature product.
BUT… I’m running it on rather heavy Win 10/64bit Pro machine I use a lot for photographic post processing. With s/w like Nikon ViewNX-i (my original RAW converter), lots of pano stitching with PTGui Pro and PS CC 2017 for more common PP.
(No, I hate LR because of the database dependencies)
The real ‘but’ I have with RT 5.3 is its lack of speed, sorry to say.
My machine is a i7 980x CPU running @ 4GHz, 24 GB RAM, 3 x SSDs for OS, scratch and swap disks. And several TB’s of HDD for image storage + R9 270x graphical card for GPU acceleration with PS CC and PTGui.
RT 5.3 takes a long time to start, almost 50 seconds or more and e.g. clicking on the ‘preferences’ button adds another 30 seconds wait. And a few seconds after I click on ‘preferences’, the rawtherapee.exe PID gets status ‘not responding’. (?) while the rest of my computer is idling…
And yes, I’ve already tried reinstalling RT 5.3, clearing its cache directory; but to no avail. Even starting in a empty directory.
When RT 5.3 is starting up, there is hardly any activity to see in the Resource Monitor. only 2-3 % CPU util, very low disk I/O, hardly any network I/O, and lots and lots of memory not used.
So what is RT 5.3 doing, what is taking so long??? Any ideas? Even starting up PS CC 2017 with a 2GB TIFF file goes faster
What might be going on?
Because this way it’s almost impossible to explore the RT 5.3 capabilities.