There were fewer truly bad games than I expected. Only two, Paranormal Psychosis and Dungeon of Gain, were actually bad. The former is a piece of shovelware by the notorious Digital Homicide, and the latter is apparently a very shonky port of a flash game.
Four others, prog.1, 7 Mages, Vermillion Watch and Purino Party were executed at least reasonably well, but failed to hold my interest. The limitations of the format I'd chosen became evident there: I rated them as "refund" not because they were bad games, but because I personally did not want to play them.
Finally, two games, Champions of Breakfast and Affairs of the Court: Choice of Romance, earned the "keep" verdict, being funny or interesting enough to make me keep playing. They were not the most polished offerings, but they were clearly the product of someone who cared about what they were making.
Though I did not play as many games as I intended, my preliminary conclusion is that Steam is not actually being buried under a mountain of rubbish - there are simply a lot of different genres and audiences.
I had fun doing this, and in fact plan to do it again, on a day chosen to be more typical in terms of number of releases.
If you want to watch me play through the games, you can click on the individual titles to see the embedded play and review, or use this handy YT playlist for the whole lot.