I upgraded from 4.8 and for the most part I think it looks good, however I am noticing some strangeness with my programs.
I have a series of programs that are used to operate my vertical blinds that are controlled via Insteon switches, and read state from an integer variable. Initially after the upgrade they seemed to execute and read/set the state variable as expected, but they would not operate the Insteon switches.
What ended up fixing it was going through each program step and clicking 'Update', then clicking 'Save Changes'. What's interesting, is when I saved, it seemed to enumerate all the other programs and refresh the status. After that the blinds programs are working, however I haven't tested everything else yet. I am not certain at this point if I really needed to update each program step, or if it would have been enough just to save changes.
The other remaining bit of weirdness that I'm seeing is that the displayed program state, both in the Summary and Details view, does not seem to be refreshing in real time. Although it's been awhile since I was in here, I don't recall that being an issue in 4.8. In 5.3 I'm finding that the state updates correctly when I manually Run (If), but I have some programs that call other programs, etc. and the displayed status seems now to get out of whack. Things seem to be running correctly, so I think at this point it is just a display issue in the Admin Console, but I thought I would mention it anyway.