I personally like them, but they aren't for everyone.
You need to like shooters, and I'm not talking about modern one's like area 51, I'm talking ooooold one's like hogan's alley and duck hunt. The reason behind this is the games have little to no randomness. And like duck hunt, you'll play it for a good setting and then won't want to play them for quite a while.
Also getting directly from dl is a tad expensive. You can regularly find them on ebay with a buy it now option for 1/4th of the price.
Also be warned that these games aren't front-end friendly. They start in windowed mode and there isn't any way to save settings (fullscreen being the only one of any merit.) I made an auto hot key script for mine so that they switch to fullscreen once I load them up though so it's not that hard to work around.
And finally you need a lightgun. If you don't have a lightgun then forget it.