First, actors are too old to pull off convincing and engaging what should be larger-than-life real life mobster/criminal characters. There is no amount of blurring or make-up artistry that helps in this case. The age reversal digital technology didn't work in this film, it only showcased the issue. Robert De Niro can’t walk the tough speak and his fight scenes are embarrassingly stiff and exhausting to watch. His tired overused scowl looks more like grumpy old man.
Joe Pesci is sadly gaunt and looks hauntingly old throughout the movie. He is still a masterful actor, but much past his prime for this role in this movie. Al Pacino is another veteran primo actor but is miscast at this time for this role because of his hunched over posture, slow awkward movement, aging face and physique.
Second, this is a bloated script. 3 hours is difficult even for an epic film, but this is just uncomfortable, painful.
It's a tellingly sad (nearing) farewell to Scorsese by making such a miscalculation, who made the decision to cast these veterans purely out of nostalgia. These misfires heavily impeded what could have been a great movie.