This game is a classic that broke new ground and can be a very challenging game. Combat is quite lethal. If you have any interest in TBS, or RPG, you'd have to be insane not to buy this for the price.
My only caution: the original release (the 1.0 that I have on CD from way back when) is very buggy (esp in latter game). Most likely the GoG version is the latest patch, but I'd make sure about that before you start off on a long game. Once you get way into it, it can be quite disheartening to realize you are working with a buggy pre-patch version, and the idea of replaying after patching.