Dino Run has a special place in my heart as the first video game I ever played on my parents shitty old Windows Vista computer, but does it hold up today? Kind of. It definitely has a lot going for it, the music is great for a flash game and the "doom" does a great job of being terrifying as balls and constantly keeping you on your toes. The games main issue however is that it's incredibly unresponsive, jump height feels totally arbitrary and as a result some of your mistakes feel kind of bullshit, which is kind of a problem when you're always 4 seconds away from death. With all that in mind I still like it, I wish the multiplayer was still active, I had a lot of good memories with it.
I really loved the original flash game, I played it a ton as a kid and I keep on coming back to DX. It seems like they removed the multiplayer feature early last year since the company hosting these servers sunset them which is saddening, but not their fault.