Pretty great when I played it. The server has had less people now at a time. Like 50 people I think. It was over 100 per round when it first came out. Had fun grabbing random D class people to bring them into peanuts enclosure so they can clean it. Random power outages made peanut escaping possible.

If you aren't familiar with Space Station 13 then I can describe that too since the SCP server is based on this. This video here can easily describe the game and I'll give a shorter explanation beneath too

https://youtu.be/nLAHBexJxrE

SS13 is a free online game where you are on a space station and can choose from numerous jobs to do during your round/shift. Stuff like security guard/cook/doctor/miner/virologist/scientist/roboticist/chemistry/bartender/gift shop worker/janitor/The Clown. Each of those jobs have their own mechanics that can go extremely in depth and it's fun to learn it on a job you enjoy.

Every round there will be antagonist picked from the players to be something like a traitor/vampire/changeling/demon/syndicate attackers/Skeleton pirates or even more. The job of the security team is to arrest/kill all the antagonist which can be hard since the antagonist have strong abilities or can buy a shit ton of wacky/lethal items from a machine like the traitors.

People have adapted the code to run their own servers based off properties like Aliens Vs Predators/Fallout/Warhammer/SCP. The AvP one is usually the most filled because it's gameplay is great. It's called SS13 Colonial Marines and totally worth a play too. That video I linked at the top contains gameplay of it.

When I can get to my PC in a bit I will find the SCP server information for you. Everything is completely free too. I've spent over 1000 hours in SS13 just in a single server since I began playing.