I think the missing delimiters and significance of whitespace bit me once or twice the first couple days I used Python. That ended after I banished tabs and turned on Python mode: in the same old editor I have been using for the last forty years.
Just to be clear, my Python code works just fine. And I use IDLE, straight out of the Python distribution, so it's not an "editor thing".
It's in reading and (especially) debugging, and especially when it's someone else's code, that Python's block delimiter mistake becomes very apparent. There's just no way that the visual
absence of something is as clear and quick to recognize. This is particularly bad with nested loops. One of the things I had to write in Python recently was some matrix manipulation code, and the nested loops where a pain for everyone on the team. I lost count of the number of times one or more of us was carefully examining a line of code in the wrong loop because the visibility of the indent level was affected by your angle to the screen - if you weren't straight in front of a monitor it became very easy to misjudge which indent level you were tracking by eye. Utter insanity! And so easily avoided, as has been done in other languages for decades. This was a completely avoidable error in language design.
It also doesn't help, if you're going to rely on whitespace, that the default indent is just four spaces. I like tight indenting when block delimiters are in use, but when whitespace on the screen is all you've got, four little spaces makes things just that much harder. Particularly in a team environment and it's not YOUR screen so you're off-axis.
Finally, Python isn't even consistent in its elimination of block delimiters. It actually has an OPENING delimiter (the colon), which basically substitutes for (say) the open brace in C, C++, Java, etc. But Python's closing delimiter is - wait for it - a
correct number of spaces from the left edge. Which is a number that varies depending upon where the associated colon happens to be (or, rather, where the line that contains that colon happens to start). And it's up to the
user to line everything up, visually, through blank white space across potentially many lines on the screen, to avoid (best case) compile errors or (worst case) unintended code behavior.
All of which could have been easily eliminated with a closing block delimiter. And that wouldn't have even been a new concept in the world of programming languages. Unbelievable.
EDIT: A good related question to this topic is "What problem were they trying to solve by eliminating the closing block delimiter?" Honestly, how many times have programmers pounded their keyboard in frustration and shouted "My life would be so much better if there was a language out there that DIDN'T require a closing block delimiter!!!" I've said, and heard, that complaint precisely zero times.