I disagree. I think the advancements made in recent times - as Roogle's mention of Avatar in particular shows - have been immense and they show that actors are not required. CG characters are capable of getting an emotional response. Hell, even blocky little sprites were. Why wouldn't the more realistic characters shown on video games today? It's the writing that is important. Sure, if the faces are incapable of showing any emotion, it can be tricky to pull off an emotional response. But we're passed that now - character faces
are capable of showing emotions. Also, with customisable faces and whatnot, actors can't adjust in the way CG can. This applies to Mass Effect in particular, which you mentioned.