If you want my opinion, consider getting the Half-Life 1 collection. It doesn't include source, but it does include Opposing Force and Blue Shift, two really interesting expansions/spin-offs. Not only will you save yourself a couple of bucks (as opposed to buying Source then Opposing Force and Blue Shift), but you will also be able to play the original version that everyone experienced way back in the day. Plus, you get access to some pretty sweet mods, and if you plan on getting Counter-Strike or Day of Defeat, install times will be way shorter.