I got mine about 3 weeks ago, and have been nothing but thrilled. No DSE, tiny amount of blooming in super-dark screens with small bright spots, but perfectly acceptable. I have heard people complaining about the built-in sound system, but seriously people... at least get a sound bar. I don't think anyone in their right mind expects to get decent sound straight out of a TV anymore. As for upscaling content, I think it does a fine job. 720p content looks very very good, and even 480p content looks decent as long as the source isn't overcompressed to start with. Of course if there's any compression artifacting present in lower-res content, it will be very noticeable when you blow it up on such a gigantic and discerning screen.
The only complaint I have has nothing to do with the hardware or even the Roku TV OS, bit with the Netflix app. Most Netflix content plays back fine, but certain hyperactive material will make the system sluggish with audio & video out of sync, going into multiple sessions that look like buffering (not due to lack of bandwidht) requiring a reboot to get things working correctly again. My wife wanted to watch the Taylor Swift reputation stadium tour - I can't seem to get more than 10 minutes into the thing without having to reboot the TV. I have read several other complaints about the Roku Netflix app, so I can only hope that they get it fixed at some point.
I know that the correct answer is to use an external appliance for my content, but I'm working my way into that. My AVR doesn't support UHD, and I have no gear yet that outputs UHD content anyway. So, it's Roku TV all the way for UHD content, then all the other stuff (PS3, PS4, Xbox360, Xbox One) is switched through the AVR into a single HDMI input on the TV. Optical out of the TV into the AVR does quite nicely for Dolby Digital, etc.