Agreed. Lifehacker's usefulness has diminished significantly over the past couple years. Besides the articles, what made Lifehacker so great in the past was its community of smart people willing to share great tips. Many of these people have left, largely due to the horrible design changes pushed by Gawker.
The average article quality used to be great there, especially for niche apps/programs, the "hive five" feature, and detailed how-to guides. There's still some great content on there - like you can see in an aggregate article like this one.
However, the average article quality has declined significantly. Once Gina Trapiani left, I noticed a drop in quality. The awful, Gawker-pushed redesign hurt too, probably turning away some of the more valuable members who contributed great stuff in the comments like you noted. If lifehacker was an independent entity (or even an autonomous one like Reddit within Conde Nast) it could be fantastic. Not possible while Gawker is pushing it's media properties to a race to the bottom in search of traffic though. Gizmodo has gotten significantly worse too unfortunately.
Are there any sites that have risen to take its place? I think there's a lot of value in a site that does the sort of blogging Lifehacker does, but in a more concise and useful manner (like they used to).
I've seen some of the past top commenters on How-To Geek and Ars Technica forums. But there's nothing that really replicates the old Lifehacker. Reddit's LifeProTips might be good eventually, but there is a significant amount of noise since it isn't curated like a blog.
Usually what I do is google specific things that I know Lifehacker is likely to have good content for: "lifehacker + ThingIWantToDo", e.g. "lifehacker + automated media centre" or "lifehacker + hive five vpn".
That throws up the good, older content (sometimes newer/updated content too) without sifting through the crap.
I used to follow Lifehacker on post by post basis. But then I realized blogs don't help much. So, I closed my Google Reader and stopped reading all blogs. I subscribed most blogs on G+ and receive a handful of posts everyday. Some of their stuff is good and most of it is so simple that it shouldn't have been mentioned. Currently, I have subscribed to Lifehacker's VIP feed which brings whole article to my Google Reader. They have been bringing interesting people through series' like How-I-work and Ask-an-Expert that I feel like missing. I just skip any article that I find to be overkill.
I agree with other HN'ers that LifeHacker has lost a lot of it's appeal - they post waaay too much. I have found myself doing two things
1. Only go to lifehacker once every few days and quickly browse to see if anything catches my eye.
2. Rather than going to lifehacker.com (the new design is absolutely atrocious) I go to blog.lifehacker.com which presents the stories in a chronological order, which makes more sense to me.
With that said, this is (IMO) a completely useless collection of how-to guides.
I don't even know what "life hacker" means to them anymore...