Some of my biases are transparent. For example, I believe that many of the complaints of Perl's "unreadability" are from people who've never bothered to learn how to read the language. You often see this from people who say "Sigils? Pfft. They're useless—mere syntactic noise!"
Linguists may disagree.
One of the early inventions in written language was punctuation. In specific, adding spaces between words (and even vowels, in some languages... yes, my history studies have come in useful while programming) makes documents easier to read. The same goes for punctuation. It's easy enough to write sentences with ambiguous meanings, depending on where you put a comma to delineate logically separate clauses. (Languages with greater riches of declensions and tenses and numbers and other forms are more flexible in word order, but they do retain some degree of poetic license. It's not all meter and rhyme scheme however.)
The basic idea behind all of these ancient inventions is that "Communicating is difficult enough without verbal and body language cues. Making different things look different helps."
To read source code, you have to be able to identify nouns and verbs. You have to be able to group related items and ideas while not grouping unrelated ideas. You need to be able to identify separate expressions as well as idioms.
One reason assembly language can be difficult to read is that its regularity (op arg1, arg2 or op arg1, arg2, arg3) precludes skimmability. That may sound odd; if you're reading code, why do you need to skim code, but it's important. Programming encompasses so many small details that you must understand the code in the small in the context of the local component as a part of the system as a whole.
Uniformity of syntax means that you have to rely on cues external to the source code or patterns of repeated details within the source code to indicate structure.
I have the same problem reading Lisp code, with its homoiconicity; the shape of the code gives me few cues as to what's different between sections of code. As well, Python's use of vertical whitespace to end blocks means that my eyes slip off of the end of logical blocks and I can't tell what happens where.
A lot of that is familiarity and personal preference (or quirks of the way my brain works). Some of that is the effect of deliberate design decisions.
If you embrace the idea, like Perl does, that different things should look differently, you reach some interesting conclusions. I don't think you can learn Perl effectively without understanding those conclusions, at least at an intuitive level. I'll write about that next time.