Just look at Beowulf, which had a whole top end studio and millions in budget, and still doesn't look particularly 'very real' Was panned by critics and the audience too. If they couldn't so it with all that skill and money, what chance does the average 3d movies by a regular poser/3d guy have ?

The thing is mocap in certain situations can be a very fast and effective tool eg for fast and broad motion like stunts or fight scenes. But for more deliberate and detailed work, it's either too rough/imprecise or runs straight into the uncanny valley. Which is why rather then pure mocap, 'assisted' mocap works much better. That's where you take raw mocap data then have it massaged by an experienced animator who knows what to clean, what to exaggerate and what to redo by hand. Done this way, mocap can become the basis for very nice (though not always technically 'real') animation. Gollum was a prime example of this and even after these many years of improvement in mocap tech, looks more interesting and believable then anything in Beowulf.