HN is also good at introducing you to different topics you haven't heard of before. However, it's up to you to do research on your own if you want to learn more about it. I wouldn't say HN is great for deep learning, but it is great for getting an idea of the general landscape. GraphQL, GPT-3, and PG essays are some things I came across here before anywhere else.
In addition, when your particular technical niche comes up you can be assured of high quality discussion.
Don't know that I've gained a lot of hard/useful knowledge necessarily, it's more an occasional source of interesting news and informed commentary, within the subset of interests HN revolves around. Have gathered some background material on specific topics of interest to me (HCI, workspaces, personal knowledge management).
I don't submit much or engage in discussion very often (this post being an exception, trying to move the consumption/creation needle a bit), but HN is an excellent resource. The simplicity of its UI and general model is refreshing, and the signal-to-noise ratio and quality of both contributors and moderation is very high.
There's also a zeitgeist aspect; I know if anything of significance happens within a range of interests, I'll likely hear about it here.
Overall though, HN is more a source of news and intellectual stimulation for me than a learning resource. It's an excellent and pretty unique one though, would miss it if it was gone.
I _have_ learned a lot and continue to use this site every day. The negativity can be mentally draining though.
Like others, I most value HN for the discussions. They‘re civil, and there are often serious domain experts participating. I like how that exposes me to quite a breadth of knowledge and opinions.
In terms of learning, it‘s very much a breadth-first approach. You‘ll hear about plenty of topics and new developments (and thankfully not just from tech), but it‘s the wrong place if you want to learn about any one topic in detail.
Also, over time you‘ll figure out the various likes and dislikes of the „HN crowd“. Like any other community, we have our preferences and biases, our little squabbles and unspoken taboos, that do quite strongly influence the topics you‘ll find here amd the way they‘re discussed.
Nowadays, I don't know. Not many things surprise me on here anymore. Some of it is surely just knowing more. But I do feel like HN "missed" some big developments. Crypto/blockchain is one example of a major trend that got very little coverage.
[Edit] I've been here since February of 2019
The most memorable things were discovering AI Dungeon from Show HN and finding out about Zen and the Art of Motorcycle Repair.
Hacker News has helped me learn to be a better programmer in mostly two ways:
1) Be enthusiastic and write honestly about what interests you. Keeping notes is helpful.
2) Hacker News is a community. The dialogue is mostly good for the topics I'm interested in. It is easier to do things and learn things when you listen to people.
Learning through participation and active application of content is going to be higher than only observing propositional knowledge and feeling like you 'know' stuff.