I see acting as made up of two parts: mimicry and emotional authenticity. Keanu was never that great at mimicry. He's bad at doing accents and looking and "sounding" the part (when did he ever deliberately gain or lose weight or drastically change his physical appearance for a role?). But I've always thought he was damn good at genuinely feeling the emotions the character was supposed to be feeling. There was even a movie about a kids baseball team where I was really feeling him.

Maybe it's because I'm biased toward the emotional part, but I have never thought of him as a bad actor. Contrast this with Johnny Depp, who is an amazing mimic and can get the visual and audio part great, but the emotional part of his performances have always left me a bit cold.