Casino is certainly more flashy and faster-paced than The Irishman, but ultimately I think the latter has more depth. Casino is essentially about a group of people who get everything they could ever dream of, but their character flaws make them lose everything. In The Irishman, it's almost the opposite. Frank Sheeran doesn't make any mistakes. He does everything he's told, but to what end? He still ends up alone, with nothing but regret. He doesn't question the the set of rules he's following, and like the soldiers in the flashback scene he ends up digging his own grave.
It's masterfully structured, and it would be easy to highlight the acting and the long list of unforgettable scenes (do I need to say more than the words shorts, watermelon and fish?). It's entertaining, a journey through American history, incredibly well-crafted and with an ending that sticks with you. I think it's quite an achievement.