I'd say Portal is a bit some to be worth it on its own. That said, it's a fantastic deal. I've been playing through Half-Life 2: Episode 2. It's amazing how well the Source engine has held up over the years. It still looks as good as FEAR, STALKER, and Bioshock and better than BF2142 and Quake Wars.
Of course the Orange Box is drawing my away from my Wii for even longer...