So, I've held off on getting these forever because of reasons not applicable to the actual product, so I'll get to the actual product. The KRK 8's are clean, crisp, and the fine-tuning capacity is perfect for most standard rooms.
One feature I love completely and unabashedly is the power save. I hate having to power everything on and off constantly, and the 30 min power off and warm kick-on help me get going quickly without any shenanigans.
As far as production, djing and general playback:
Production: I can tell when I need to take a break because they don't wear out, my ears do. If I can feel myself reaching to boost the highs I know something's off.
DJing: They've been instrumental in learning my gains on tracks more, as auto gain only does so much. Differences in bass response from track to track also comes through clearly and sometimes shockingly so. It's like a magnifying glass on tracks I thought I knew before.
General Playback: for casual listening they're mostly amazing. As per the magnifying glass comment for DJing, these have made me uncomfortable with certain albums because I can tell the production came up short for the digital editions.
Definitely worth it for the clear and defined mids, lows, and highs, and for the capacity. Definitely need a sub to get a full picture of the bass below 60-90hz. The low end roll off is reliable, but sometimes obnoxious in it's reliability for songs that I know "BUT THERE'S SOMETHING WAY DOWN THERE." That said, it's made me way more aware and helpful for getting reliable replay-able sound from my tracks.