Mostly speed, a more minimal configuration syntax, more modern crypto.

OpenVPN works fine, is quite portable and runs in user space. It's quite a lot slower, but is well-tested and can be managed with a Certificate Authority in organisation where that's desired.

I presume speed on linux? Otherwise doesn't wireguard suffer from the same peformance drawback than OpenVPN on windows (running in user mode)?

OpenVPN is quite configurable, not as much as IPsec, but still a lot, and (from what I hear) has quite a bit of code bloat. I believe that userspace WireGuard has better performance than OpenVPN.

My understanding (and experience) is that OpenVPN on windows is structurally capped at about 5-10 MB/s. I was curious of how that compares to WireGuard.

Performance issues with OpenVPN on Windows arise out of the inefficiencies of the TUN/TAP driver, not the OpenVPN software itself.

I am sure that's true, but unless there is an alternative driver I am not sure why that makes a difference.

Thomas Ptacek does it better than me: https://news.ycombinator.com/item?id=14599834