I'm a huge Lincecum fan (probably more than anyone on this board as I watch almost everyone of his starts), though $17.5 million per season is a lot for a pitcher who has had declining velocity and who last season looked liked he was done. He had a very respectable 2013 season, though I still wouldn't pay him that much per season. The one good thing about the deal is that it's only two years, so Lincecum should still be productive. I'm guessing Lincecum is worth more to the Giants than he is to another team since he's been there since 2007, won 2 Cy Youngs, apart of 2 World Series teams, and is a fan favourite.
As for his walk rate, he did keep it in check in 2013, though previously his BB rates in 2011 and 2012 were worrisome. Even his 76 BB's in 2013 aren't that low. He's still generating strikeouts and swinging strikes despite diminished fastball velocity which is the plus. He's learning to pitch with a 90 mph fastball, though I still wouldn't pay him $17.5 million.