In a word: ACCURACY
You don't want "good color" or "good contrast" or whatever. Those are boosted values. You want true to the source, accurate.
Not shiny. Never shiny.
Never HDTVs, as those are always shiny now. Values not accurate, always screwed with, boosted.
Calibration is important. I can often calibrate without a Spyder, but I also have 25+ years experience in calibration. I have special images for it, and can compare against my other already-calibrated setups. But I still have a Spyder, somewhere here. Get one for yourself.
IPS is important. Only get IPS.
Since 2005, all of my/our quality monitors have been LG, Dell, and Viewsonic. LG and Dell are always quality, for their higher end IPS monitors. Some Dell dither issues a decade or so ago, not true bits. Viewsonic was mostly a case of "even a budget company can make something exceptional" (ie, most of their items are NOT so great, aka Best Buy fodder, lower end).
Right now, I have a LG ultrawide 2560x1080 as my main monitor for editing. It took daily fiddling for about a week to calibrate, several years ago, but it's also not drifted over time. My oldest LG from 2005 has drifted some, have to recalibrate from time to time, used on backup capture system.