I'm thinking that De Niro hasn't been truly great in anything since the late 90s (circa Sleepers/Jackie Brown), and in some recent stuff he's been damn right embarrassing.
He's still an acting legend. Nothing can take that away from him. During the mid-to-late 70s, the 80s, and most of the 90s, the man barely put an acting foot wrong, but for the last two decades he's been operating on auto-pilot.
Still, The Irishman (where he's reuniting with Scorsese for the first time since the superb Casino) and The Joker sound promising.
I thought he put in his best performance in years in Silver Lining Playbook. But his last truly great performance, top notch De Niro probably 1995 with Heat imo.
Really really great? Cape Fear. After that he was pretty good in A Bronx Tale, Heat (although a slow burn of a performance) and Casino. Meet the Parents was also a superb comedic performance. So you probably have to go all the way back to the Awakenings/Cape Fear era, up to Casino/Heat.
The problem for DeNiro, and Pacino, and...though he hasn't worked in ten years and may never again, Nicholson ..is that fewer great movies are being made, and if/when they are, these guys are now too old and lesser-known for the leads.
I think you'll find with all three of those guys that they had "great periods" (say the 70's into the early 80's) and that's all they needed to coast along for decades as "prestige superstars"
DeNiro
Bang the Drum Slowly
Mean Streets
Godfather II
Taxi Driver
The Deer Hunter
Raging Bull
Nicholson
Easy Rider
Five Easy Pieces
Carnal Knowledge
The Last Detail
Chinatown
Cuckoo's Nest
Pacino
Panic in Needle Park
The Godfather
Scarecrow
Serpico
Godfather II
Dog Day Afternoon
And Justice for All
Scarface
....
Those were the "big runs" for those three guys, and then they cashed in ever after. Pacino took most of the 80's off before coming back in '89 with Sea of Love, and then got an Oscar for Scent of a Woman(Hoo-ah!) but somehow those didn't feel like great ones, though Glengarry Glen Ross and Carlito's Way DID.
Nicholson, after completing his "70's greatness phase"(with Cuckoo's Nest and an Oscar) kept going away and coming back, landing in blockbusters like Terms of Endearment, Batman, A Few Good Men, and As Good as It Gets and keeping his star shined pretty much for all time. But they weren't like that "prestige 70's group."
I recall with DeNiro that he seemed to be an "art house movie" guy for the longest time, and then he slowly started to appear in "entertainment": The Untouchables(a cameo as Al Capone.) Midnight Run(a buddy cop/crook movie with Charles Grodin.) By the time he did a small part as a father-figure arson cop in "Backdraft"(1991) I saw it: DeNiro would now be capable of getting big bucks for lesser parts.
And: despite his having that 70's-80s run as his classic period, he perhaps became more popular than ever teamed with Scorsese and Pesci for GoodFellas and Casino. Which allowed him to anchor Heat with fellow coasting prestige superstar Pacino.
I think DeNiro was spectacular in his small-but-constant role as a lethargic but dangerous ex-con in Jackie Brown. He's a comedy character in that -- very funny in his deadpan nothingness, even when he turns deadly at the end. Very sexy, too, what with that beard and stache combination. Middle-aged stud.
Others on this thread are more familiar with his later work, but its true: he's done too much hack work for the bucks. Rocky and Bullwinkle. Still...he seems to be working more than Pacino..and Nicholson doesn't work any more.
Since I'm not familiar with his later work, I'll pick "Ronin" from one year after Jackie Brown, as DeNiro's last really good perf. Copland was more of a cameo.