There was not even single line of documentation all of the few files I peeked through. In several of the technology companies I worked, code without proper comments along header was considered to be a garbage and not worth a single cent. There are lot of philosophy behind making a good coding practice which I can not start over here, it is even taught in CS101.
I also read the source code. IMVHO (based on 40 years of computer experience) code is pretty reasonably commented.
I looked particularly in src/primitives, src/rpc, src/wallet and some other subdirs.
In .h files that contain data descriptions, some structures have description of each field.
After reading those files, .cpp files can be easily read and understood.
well, i did not find it reasonable. i have less than 15 yrs exp, but imho, experience does not really count much after 5-6 yrs. In fact, if particular engineer is opinionated about commenting and documentation is NOT necessary it seems it is even harder to have 'em change their habit because he/she becomes more inflexible as person gets aged.
OK This is the war of personal opinions. I can understand this code with this amount of comments and you cannot.
The quality of software is determined.
1. Correctness; 2. Security; 3. Performance, not by density of comments.
And again IMHO, I consider that https://en.bitcoin.it/wiki/Bitcoind is good enough documentation.