Left 4 Dead 2 runs perfectly fine on Windows 10, no problem. It's a game that's very compatible with the operating system and Valve keeps it updated on Steam, so you don't have to worry. Most players who have it installed report that it runs without needing to do anything special, though obviously it'll depend on your hardware. If your computer handles modern games smoothly, L4D2 is going to run great for you.
The only thing you might need is to install some DirectX components if for some reason the game asks you for dependencies when you run it for the first time, but Steam usually handles that automatically. If you want to make sure everything runs well when you open it, update your graphics driver and check that you have the latest drivers installed. Apart from that, it's a solid game that runs without drama on Windows 10, so go ahead and play with your buddies.