Direct2Drive (a Steam-like download store) has been running some $5 specials for their fifth anniversary, and this week is "Indie games" week. World of Goo looks the most interesting, with both Mac and PC versions available at the discounted price. Can anybody tell me whether it's worth installing D2D's software to play it? Maybe I'd pick up Bioshock too, it looks like it's still being offered at $5.