There are a few things that I've noticed that I never used to see:
* More politics. In the interest of full disclosure, I'm a crazy flaming liberal, and I still don't want to see things like the Ayn Rand story that popped up earlier today, even though I agree with it. I have plenty of sites I can go to to get political news and discussion. I've traditionally liked the fact that HN isn't one of them.
* All Edward Snowden/NSA all the time. Yeah, ok, I get it. It's a big story and a big deal. But, at this point, there's nothing new to talk about. I see what amount to the same comments posted day in and day out on these threads. And it's really boring.
* Incredibly racist comments. On a number of occasions lately, I've seen people post comments that are totally unacceptable in civilized discourse. e.g.: https://news.ycombinator.com/item?id=6041616 and https://news.ycombinator.com/item?id=6005314
As a result of these, I've seriously considered abandoning HN, and likely will just like I did with Slashdot years ago. I really don't want to, and I know it can never 'go back to the way it was,' but the overall level of civility needs to change dramatically (and this is the responsibility of everyone in this community. Call people on it when you see it and make it clear that this is totally unacceptable).
Maybe there needs to be a new section of the website entitled "Aaron never has to click on this link" (or just "Politics"), where we can sequester (ha) everything politics-related.
Anyway, to sum it up: the community has absolutely changed, and generally for the worse. And it's our responsibility to fix it, but we'll also need some help from pg.
Metafilter, as you said, is one example. Another is the Ruby Rogues Parley mailing list (now Discourse site). I can only imagine what a HN with similar filtering-of-the-noise would be like.