I disagree about Reddit, but I completely agree about Imzy: this is the first time I've heard of it. This reminds me of all the times I've read an announcement like this about some Google service that was being shut down, and that was the first time I'd heard of it. Obviously you're not going to have a lot of users of something if people have never even heard of it.
As for Reddit, it's fine. Reddit is a HUGE site full of many different forums (subreddits), so you can't paint them all with the same brush. Some of them are really horrible (/r/pyongyang, /r/The_Donald, /r/HillaryClinton) and full of vile people, others have IMO overzealous moderators (/r/politics), but there's literally hundreds of thousands of subreddits so there should be some on there to suit whatever odd interest you may have. There's one for my car, for instance, which sometimes has an interesting posting. There's /r/EarthPorn which has really nice nature photos posted every day and where I learn about great places to visit and hike. Every subreddit is totally different, with different moderators; some totally suck, others are pretty handy. It just doesn't compare with a site like Slashdot at all.