Yeah, he wasn't better in the books. He's flat and uninteresting there, too. His entire function was to serve as a Saren-surrogate, and that was a well-intentioned but misguided goal.
Fact is, TIM and the Reapers were plenty villain enough. They were trying to create a 'personal' conflict like Shep had with Saren, but it fell flat. Saren was an awesome villain because he was sympathetic and also awesomely villainous-- and if you read the books, you realized that he was xenophobic and racist with regards to humanity but not EVIL, and his indoctrination just exacerbated that existing issue. Plus, his voice actor was off the fucking hook.
Kai Leng just consistently did stupid shit for no reason, and could barely beat a critically ill drell (admittedly, that drell was THANEOMGBADASS), but still. Seriously?