It is very, very good. Much better than Half-Life 2, and because of its original status as an afterthought in the Orange Box, it still feels subversive to this day. It's got great control and it very much set the blueprint for the "Purity of Design" ethos that so many indie games carried onward. Still, it's not as innovative as it was set out to be and it's still very much a niche genre that many people wouldn't be able to enjoy unless they were highly knowledgeable of the medium, so it's not the "ideal intro to videogames" that many have claimed it is.