I'd find it hard to say 'That's a bad list' because it all depends on what games you've played, and what you're opinions are. Actually, it's not that hard. That's a bad list. The voice from Portal? The Lich King? Give me a break, please.
I'd agree with Sephiroth and Bowser to a certain extent, except that Kuja and Kefka were far 'better' Final Fantasy baddies, and Bowser is such a likeable character to play in the Mario spinoffs (Kart, Smash Bros, Tennis etc.).
Bohan I've never heard of, and Andrew Ryan and Wesker I've never encountered due to not playing their respective games enough. Bison is a weird choice, though, since the Street Fighter games have very little story or characterisation to develop a hatred for him through, and the G-Man is just a boring rhetoric machine. Ganondorf is a decent shout, even though I haven't played all the way through Ocarina of Time.
Names I'd include on this list would be Ridley from the Metroid series, the Nemesis from Resi Evil 3, Kane from C&C (good shout, Fist), Saren (and, by extension, the Geth) from Mass Effect and Jericho from Driver 2, among others.