Very underrated. Out of the fighters he has fought, Moorer considered George to have the most tricky defense, and it's worth noting that George was using mainly the long guard/extended rear hand against him, which is a bag of tricks from his first career (punch traffic, hand traps, leverage guards, posting, parries, framing etc.)
Yes. George was a walking master class in all the skills that Rollin here identifies, which are among the best techniques and are seen in other fighters rated as the best defensively, e.g., Loma, Floyd. To that list I would add "redirections," especially that toreador move that worked so well on Frazier. So, other than the fact that he seemed unable to move his head, excellent.
His go to defense against a hook he did not manage to proactively stop was a duck, but other than that yeah, not much head movement.
I think his cross armed defense in the comeback was more effective than his methods in his first career. But that’s just an opinion
1st career he was very good at catching, parrying, and redirecting single shots. It might have looked like he was open, but he could easily swat away many guys shots or frame them and set up shots of his own. It was a very active guard and it allowed for him to "interrupt" what his opponent was doing. The main weakness was against guys who could throw very fast combinations or shots from unusual angles, then getting out the way before he could take them back. I also think a guy who had long arms and a fast dash in could frustrate him by going high and then low very quickly. Either way, it was very risking throwing combinations against Foreman since he could turn a fight around instantly with one punch. 2nd career what changed was primarily hsi pacing and ability to relax and conserve his stamina. The cross arm block proved very effective since he had big arms and made it very difficult to nail him in the head when he went in his shell. The main weakness was that he couldn't fire back as quickly as his original guard, and he had grown even slower with old age making this weakness even more apparent.
Slightly underrated defense. It depends on the type of puncher he Is facing as well. Straight punchers give him more trouble than a hooker or infighting.
George Foreman in both careers had a very porous defense, it is just when he started his pro career in 1969, George was more of an offensive minded fighter whose weakness is that he often got tagged because he was more of an offensive first type of fighter, this was evident when he dethroned champion Joe Frazier on Jan 22 1973 in Kingston, Jamaica. Foreman did eat some Frazier left hooks during his short easy win. In his comeback in 1987, Foreman was much slower but a more cautious fighter with extra weight on board, he did take more punishment as evidenced against Alex Stewart when he resemble the mythical Sta Puff Man after the win.