CBI 5: The Brain is actually CBI: The Greatest Hits. All ideas, including the climax twist, have been rehashed from the previous films. SN Swamy tries to contemporize one of the kills, but once certain things become evident in the more briskly paced second half, I realized that he was only harking back to another script of his (from the '90s) starring Mammootty himself. The film is exposition-heavy, and those vague close-up shots, which may have worked 15-20 years ago, fail to work here. The setting, the playout of events, and the not-so-novel idea of the killer having accomplices are all picked up from the earlier entries and Swamy's other works. But the most disappointing factor here is the motive for the killings - not only is it the weakest element but it also struggles to firmly bind everything together. Even when there were loopholes and questionable climaxes in the earlier ventures, at least the murderer's motive was one that made sense.
P. S - It was a pleasure seeing Jagathy Sreekumar (as Vikram) for that wonderfully effective but short scene. Even Mukesh (as Chacko) showing up for just a couple of scenes felt nice.