I am going to go against the grain here and say I am pretty sad about flash dying. Yeah it sucks, is a security risk, etc etc, but there is some (basically illegal if I am being honest) streaming content that only is distributed via Flash.
In 2011 I could stream any football game on TV to my phone thanks to Flash support. It bailed me out when my favorite team played during a wedding I had to go to once. Today I no longer have that option. Yes it ate my battery and yes it was laggy, but I had the option. Or I think about web radio- almost any local station has some sort of flash plugin to stream content via a web browser but often you have to pay to stream that same content through an app. Or how Hulu still has some free content on the web browser, but mobile devices only can access via paid Hulu Plus. That sort of thing.
The only other thing I will miss is WMC. I never really used it for long periods of time, but I really like that a legitimate way to get content recordings existed if nothing else as a form of plausible deniability to less legitimate ways of content acquisition. Kinda like how I have always said that the pot smoker's best friend is a tobacco smoker even if they themselves don't smoke tobacco, because tobacco being legal allows stores to sell "tobacco" pipes (that we all know don't get used for tobacco). It is a convenient cover.