Another Debian Testing user here, I've been running it for I-can't-remember-how-long and genuinely can't recall the last time there was a showstopper. My use case is very standard though, no gaming or running servers or heavy development. Recently rolled up to Trixie with no issues whatsoever
Homeworld and Half Life for me: both were just awesome. I spent a very long time in both.
My tip would be to make sure of your storage partitioning: Keep all your data entirely separate from system stuff then you can swap out distros pretty much as and when you please. Also: Debian stable, then testing when you're comfortable
Already been said, but that really is so cool 😎
AC/DC, for another