Final Verdict? If you liked the first two, you'll like this one. It's a pretty quality adaptation of a wonderfully complex and interesting manga series.
"For those of you who would rather avoid any and all spoilers concerning the third film in the 20TH CENTURY BOYS series, let me state here and now: if you at all enjoyed the first two movies you will enjoy the third and final film just as much as– if not more than– the previous. Director Yukihiko Tsutsumi provides a satisfying and all-encompassing finale to a trilogy that had a great deal of sub-plots and loose ends to tie up. Against all odds, Tsutsumi manages to provide the sort of closure that few manga adaptations are granted. So let out a big sigh of relief; 20Th CENTURY BOYS 3: REDEMPTION (20-Seiki Shonen: Saishusho-Bokura no Hata, 2009) does not disappoint."