Linux

Lucky guy, I ordered it to Germany and they wouldn't let me use the non-eu warehouse (so they can get rid of their overpriced stock I'm guessing)

Stopwatch - can't be minimised, can't see the time while it's open, restarts when you get a notification (the fixes have been sitting in the PRs for years)

Notifications - don't get cleared when you clear them on the phone, clearing them on the watch doesn't close the notifications screen, answering your phone through the watch doesn't dismiss the call notification

Heart rate monitor - essentially useless since it can't take periodic measurements, doesn't work great unless you're wearing the watch on the inside of your hand, but at least they've managed to finally read the sensor docs and program it correctly

Step syncing is a massive pain in the ass and often requires you to "manually" sync them by walking around while keeping both devices active

Battery barely lasts longer than a week even with infrequent wearing (and that's a massive improvement over the previous 3-4 days max)

Lift to wake up usually acts more like shake to wake

The UI is pretty bad overall

There are like 2 half decent watch faces

Horrific weight distribution and the shitty strap make it feel 10x heavier. Like, my automatic is almost 2x its weight and I barely feel it, while this crap is constantly reminding me it's there.

The CPP OS doesn't let you chose what apps to activate nor does it have any way to load your code aside from compiling everything

Updates are only mostly headache free if you use specific PC software. Keyword is mostly, I've had some updates take a bunch of attempts to install.

That's just from the top of my head