You can go back and play them again right now if you want, they're available on nolfrevival and since nobody knows who owns the rights to them nobody is bothering to contest the copyright.

The gameplay does not hold up well. I still have it installed and will make another attempt to get through it at some point but it was not particularly fun to play. Many old FPSes do feel terrible nowadays in truth, we've come a long way in that particular genre and such a large part of the enjoyment of those games is in the feel of the gunplay itself - which has typically aged like milk.