Not sure if it is a case of benefiting from low expectations (due to all the negative reviews), but I didn't find the app to be all that bad. I see a lot of confusion on features existing or not existing, so I thought I'd summarize my experience as to what actually exists, as of 12/03/23:
--4K: This one is a bit tricky, and the confusion is understandable. The bottom line is that 4K only exists for HOME Bruins/RedSox games. I'm guessing this is a logistical issue, and only the Garden/Fenway are equipped with the proper stuff that can't be controlled on the road. But 4K does exist, however with the following caveats:
--4K is not a 24/7 channel thing -- it is only for certain games/events, which is par for the course for any service's 4K, not just NESN. But the two 24/7 channels (NESN/NESN+) are FHD (1080p), and seem very good quality streams to me.
--Only Bruins/RedSox games are available in 4K, so other events like college-level games or regular NESN shows are NOT in 4K, since those venues are likely not equipped for it.
--Again, even for Bruins/RedSox games, only HOME games are available in 4K, likely since they don't control the equipment on the road.
--When a game is available in 4K, the pre-game and post-game are also available in 4K.
--On-demand: I didn't see any games available on-demand, which I personally don't care about, but thought I'd mention it. I only see 3-minute summaries of Bruins/RedSox games on-demand, and only for games that NESN covers, not nationally-televised Bruins/RedSox games on other networks. On-demand has many of the "shows" on NESN/NESN+, but no actual games. I only joined at the start of hockey season, since I really only care about the Bruins, so not sure if it is different during baseball season.
--Pause/Rewind/FF: This exists and works fine for me. Not sure why I see recent reviews stating that it doesn't exist, but it does for both NESN/NESN+, and works fine for me. You also have the option to "start from the beginning" of a live game.

In general, the streaming itself works very well for me, and I haven't experienced any buffering at all. The live NESN/NESN+ streams and 4K events all start in a second or so, and stream very smoothly and high-quality. And pause/rewind/ff all work fine for me. My internet bandwidth isn't anything huge for nowadays -- my speed tests are usually between 60Mbps and 80Mbps. And I will say that the regular FHD/1080p streams are very good quality. I have a 43" TV screen, so the difference between a good-quality FHD/1080p stream and 4K isn't that big anyway. If you have an 80" TV screen, then it would make a difference, but 4K isn't a huge deal on TV screens under 50" (in general, not just with NESN). My guess is anyone with buffering issues either have underpowered hardware (CPU/memory) or internet bandwidth, since I haven't experienced it. I have the "Max" version of the FireStick 4K, which has more memory and makes a difference with all streaming and general use.

Some things missing from the app:
--Unless I'm missing something, there is no channel guide for NESN/NESN+, which just seems odd and obvious. So you need to use the phone app or a computer separately for that.
--A tab that just shows scores for all desired teams or at least all local New England teams (pro and college). Their phone app has this, so not sure why the TV app doesn't have it.
--The interface/layout isn't horrible, but could be better/cleaner.

Brand	N/A
Rating	2.2 (137 ratings)
Price	$N/A
Category	Sports

NESN 360