It's worth it just for Crusader Kings II
The latest Humble Weekly Sale is a cracker, putting up a bunch of Paradox Interactive's biggest titles. Pay what you want and you'll get War of the Roses (along with access to the War of the Vikings alpha), Warlock: Masters of the Arcane, Leviathan: Warships, Dungeonland and The Showdown Effect. I've spent quite a bit of time with most of them, reviewing all but Dungeonland, and can confidently recommend them all.
The most notable addition is probably Europa Universalis III which, while not quite as good as the latest iteration of the series, is pretty bloody splendid, and will certainly eat up days of your life.
Pay more than the average (currently $5.80) and you can grab what are probably Paradox's two most popular titles, Crusader Kings II and Magicka. It doesn't appear to include the many DLC expansions -- which are quite robust -- but the core games are still grand.
As a bonus, you can splash out on 48 Paradox titles, all on Steam, for $125. It's a lot, but a bargain for that many titles and, as always, you can donate your payment to the American Red Cross and Child's Play.