Half-life was released in October 1998. Everquest in March 1999. Warcraft and Warcraft II came out in 1994 and 1995 respectively, but they didn't start infringing on CF territory until June 1996 when Battle.net was released.

All of these (and other titles like them) are much more widespread than they used to be, to the point where it's viable now to hook up to a random server online and start fragging away. I'm not certain, not having been a part of that "scene" at the time, but I don't think this was the case in 1998 when Half-life was first released. You generally had to assemble a group of players on your own and find your own LAN to play on.

As for other games that compete with CF, I've heard people mention Diablo II, Neverwinter Nights, Guild Wars and City of Heros in addition to the most recent World of Warcraft craze.

Carrion Fields, for its part, came out in Spring 1994, so it predates the earliest of these by two and a quarter years.

My take on the whole "graphical competition" argument is this. It isn't that existing players are defecting in order to play graphical online environments, it's that potential new players are showing a preference for these alternatives instead of text-based environment (with an extremely high learning curve) like CF. There is always going to be player turnover. People leave, new people arrive. In the past the outflow has always equaled the inflow; that may not always be the case.