I own the cd-rom DOS version and the "win95/98" version.
I had played the demo years ago, but I bought the game after I had gotten into Dark Forces II: Jedi Knight to see "how it all began."
While I liked the idea of DF, I felt the first couple of levels were somewhat boring.. but the game got MUCH BETTER as you went on, and I enjoyed playing it (that last level was somewhat frustrating though, with the lack of mid level save).
The other thing I really liked is that there was already a large library of user-created content (especially maps) to browse through when I bought the game.
I will confess that I felt ripped off when I bought the Win95/98 version of the game. It is 100% identical to the DOS cd-rom version, except that they included a win9x "launcher" for the game (no new features, sorry) that only works if you installed the game into the default directory anyway (c:/dark/). So it was kind of pointless. Also I bought it at Hastings, and they first told me I could return it, then said I couldn't. But... it was only 10 bucks at the time, so not a big loss. But I digress.... ; )
PS: Don't bother with the PSX version, it's just slightly below the PC (goofy controls, lower res, no editing). I really want to try the Mac version though, with its higher resolutions. I wish LucasArts would release the source for this game, so that people could make it with higher res, internet multiplayer, OpenGL and stuff like that (like what has been done for Doom and other older FPS games). I enjoy the DF mod for JK2, but it's not the same...