I didn't like Ultimatum. I enjoyed the early Ultimate line but I found Ultimatum lacking and rather over the top.
That being said, I think this is one of the truest scenes of Ben Grimm I have ever seen. He knows his best friend is a good person, misguided and often distractable, inside he is a good person. Ben has spent his whole childhood and life in an attempt to protect Reed from choices that would break him or hurt him. So he, the "Monster" on the team, as is a repeated theme through out the Ultimate line, protects his friend from becoming like him with one last action. Out of all the suck and needless bullshit of this line I have to say this one moment is something I find completely IC for Ultimate Ben Grimm, and even something I would see 616 Grimm doing.