Yeh I guess, Half-Life 2 is quite fun, HLDM2 is good for laughs every now and again with the grav gun, and DoD:S never played.
Make sure your comp can handle it before buying though...
That is what it seems like you are asking, is it worth upgrading my comp. Becasue for 3 games and mapping capabilities for only 20usd as you say, is a great deal, so I can't see a reason not to take it unless..