I like the idea of OpenBSD. However I have been burned many times over the years as they have decided repeatedly that it is okay to make breaking changes to PF’s rule syntax. This means if you’ve installed a dozen PF firewalls for customers, you get to go around reconfiguring all of them. The nature of these types of fixes is particularly problematic and often requires on-site work where out-of-band access is not available.
It also means innumerable copies of “The Book of PF” mentioned are now paperweights, along with hundreds of articles. Readers of such articles get to play a game of “guess whether the advice in this article works or breaks PF”.
I have many problems with Microsoft, but their support for backward compatibility is something they’ve gotten right. I am hesitant to criticize volunteer programmers, but they should take a page from Microsoft’s playbook here.
I no longer use PF because I can’t worry that any day they’ll roll out yet another update that breaks my configurations.