Aye, that is my one sizable complaint with dead space, no character means no empathy. I also hate it when they do that in RPGs, make it so the main character never says anything so you can be 'more a part of the story'.
Here's the thing game devs, i don't want to be part of the story because i'm a boring geek, if i was part of a story it would be crap, i want to watch people with deep and interesting personalities partake in an adventure/journey. Hopefully they will have learnt from this in dead space as it is the complaint i see voiced most. What annoyed me the most is that Isaacs personal log was really well written, if you read it (which you never really needed to do) he added his own personal thoughts and opinions, all of which i thought were insightful and/or realistic for the situation he was in. If only they had just had someone do a voice over of those at the start of each objective it would have been enough.
Rumour has it that the sequel will not feature Isaac, so hopefully they'll also get a voice actor in to replace the mute.