Granted had I watched any other film but Boogie Nights after I had watched Raging Bull I would have never realized the structural similarities between the two, but I did, so here we go.
Both features start off with their central characters Jake (Robert De Niro) and Eddie (Mark Wahlberg) just barely staving off mediocrity. But success follows shortly after with Jake meeting the new love of his wife, current wife be damned, Vickie (Cathy Moriarty) and Eddie meeting Adult Film Director Extraordinaire Jack Horner (Burt Reynolds) and becoming an adult film star with the moniker Dirk Diggler.
Jake LaMotta with the aid of his brother Joe(Joe Pesci in arguably his best performance ever) starts whooping ass and beating every opponent that comes his way, even perpetual foe Sugar Ray Robinson. With the money pouring in LaMotta gets married to Vickie and starts a family. Dirk is quickly becoming the toast of the pornography world and a major component of Horner's legacy.
LaMotta eventually gets his title shot after making a deal with mob boss Tommy, but it comes with a cost as LaMotta has to take a dive. Once at the title-fight Jake absolutely demolishes Marcel Cerdan taking the long awaited Middleweight belt for keeps. Dirk, after consulting with Jack, gets his own James Bond knock-off franchise and the money keeps rolling in.
But of course as is with all Martin Scorsese and Paul Thomas Anderson films there can be no happy endings. LaMotta retires after losing his belt to Robinson and opens a nightclub. At the nightclub a fourteen year old girl is served alcohol and "introduced" to some of LaMotta's acquanitances. Vickie leaves him and takes full-custody of the children. Afterwards LaMotta is locked up for failing to obtain the $10,000 he needs for bail.
Dirk becomes engaged in a major coke habit and decides he is a star in his own right shunning Jack and branching out with Reed(John C. Reilly) to become musicians. Their mutual friendship with dealer Todd(Thomas Jane) becomes dangerous as he decides to rob a producer and ends up getting killed and Reed and Dirk are running for their lives. Dirk is eventually nearly beaten to death after being jumped by a gang of homophobes. LaMotta returns to performing sub-standard comedy at nightclubs and Dirk reunites with Horner and his "family".
Knocked down, but not defeated Dirk and Jake end both films almost identically as both are giving themselves pep talks in front of the mirrors of their dressing rooms.
Both films are essentially character studies and considered the best works of each director, I personally find There Will Be Blood and Goodfellas to be each director's Magnum Opus, respectively. But that is another debate for another day.