Thanks. Looks like I have some troubleshooting to do.
EDIT: Out of the ~15 games i tried now, the ony game that started and finished the content verification is Binding of Isaac. The rest is just doing nothing. What is going on?
EDIT2: Just tried something on my laptop.
I had an older version of Steam installed, verified game chache of Hotline Miami just fine. Then I was prompted to a client update, installed it, and now it also stopped working on my laptop. Looks like the latest (non-beta) update broke that functionality for a lot of games on my end, on two separate PCs.
Strange. Opt into the Steam client beta; perhaps it'll fix the issue.