Super Bunnyhop spent a year with the Index and did a very good, comprehensive review, and I gotta say I agree with most of it.
I was playing a bit of The Room the other day and I found myself starring at a piece of oak furniture up close, astonished when I realized I couldn't see a single pixel. No screen door effect whatsoever! When I looked at a white paper later on I noticed slight screendooring tho, but it took some effort to see it. And yeah the tracking's very good. The headset is very comfortable and the sound's good.
But there's plenty of downsides as well. Even when coming from the basic Oculus (non-S) Rift there's clear downgrades. With the Rift I could just strap the thing on my head and the app would boot up automatically and I'd be in VR. With SteamVR I gotta press the button to start SteamVR first, and then it's really a crap-shoot whether it starts or not. Often I'll have to un-plug and re-plug some cable, or select the "Restart headset" option before I get any visual in my headset. Getting sound is an issue as well, often I'll have to switch audio source manually in Windows before I hear anything in the Index. And as for the Knuckles controllers? Grabbing things with these kinda sucks. With Rift controllers there's a clear grip-button where there's no ambiguity about whether it's pressed or not. The Knuckles have a completely smooth touch-interface for grip that reads each of your fingers, giving you IN THEORY much greater control. But a game really needs to be designed with these things in mind to take advantage of it, and at the moment pretty much only HL Alyx is. Which means that for every game that ISN'T HL Alyx, gripping things is fiddlier, less consistent, and just plain feels worse than when using an Oculus Rift controller. Overall I'm starting to feel the same way about the Knuckles as I did about the Steam Controller. Good idea in theory, but in practice you're better off with just a plain gamepad.