I thoroughly enjoyed this film. A warning, though; this film has a 3.5-hour run time. However, the amount of material covered, as well as the overall storytelling, justifies it.
While it starts out as a typical Scorsese mob film, a la "Goodfellas" and "Casino" (both are incredible film as well), it goes much deeper. The inner turmoil of the characters, particularly Frank Sheeran, gives these mobsters more humanity. Also, it doesn't glamorize the mob life as above-mentioned films. To see the mobster growing old and living in a nursing home, agonizing over their past, hit me on a deeper level. I truly felt sad by the end of the film.
While some would mainly praise Robert De Niro's portrayal of Frank Sheeran, the entire cast was incredible. This is the creme de la creme of mobster movie casts.
Once again, I would highly recommend this film. You may need a few bathroom breaks, but it will be well worth your time to watch.