I agree with the other replies in that I don't think the quality of Reddit has necessarily gone down, you just have to look in the right places. You probably can't get the deep discussions that you initially could, but on the other side of the coin you also can't get the vast amount of new content that you might've never come across.
You certainly do need to hide away from the top level stuff and find the sub-reddits which you can tolerate. For example, the sports reddits are awesome forums for me to visit, but the design and web design ones rarely grab my attention.
With a community of any size that can grow infinitely it is going to be tough to maintain quality. With that being said I created a site that tries something a bit different where you can only follow 150 people and the content you see are the links and posts those 150 people comment on.
This doesn't limit the amount of content you can see because the 150 people in your network will be following their own set of people and so forth so the good content should spread naturally throughout the site. In essence I guess you could think of it as a mix between HN and Twitter where you get to curate the content based on who you follow.
It's called Dunbargo if anyone is interested in checking it out: https://dunbargo.com
There are two restrictions that might not sit well with the HN crowd, but things I put in place to manage quality:
1. You have to connect to LinkedIn just so the site can get your real name.
2. The people you invite you are stuck with forever. This means you can't just toss around your invites without any thought, but instead have to consider if the person you are going to invite will actively do a good job contributing to your stream.
These guidelines make it so the site isn't for everybody, but then again I'm not trying to create a place for everybody.