Goodfellas is Scorsese's best movie when it's all said and done. He made a lot of good stuff though outside of the gangster/mob films that get all the praise.
Some movies I recommend from Scorsese.
Mean Streets - This movie is the closest thing that exists of a movie version of a GTA game, and it came out decades before the game series. Robert DeNiro's hoodlum character basically is a GTA protagonist causing chaos and doing dumb shit for fun. The secondary characters exist to give Harvey Kietel jobs, similar to mission bosses in a GTA game. It's where he earns his money (that he then spends around the city like you do in the games). If someone watches this, think of it as a GTA game and it's so much more fun.
Taxi Driver - This is the movie you have to watch today to understand the problem we have young white men in a society that hates them and constantly tells them over and over how much of a problem they are for merely existing. Travis Bickle is the original weirdo white guy with no purpose in life; poor understanding of women and dating, trying to figure things out and is willing to do something insane to discover what his purpose is. This movie is more relevant today than it was 40 years ago. We now have an entire generation of Travis Bickles who don't know what to do with their lives.
Cape Fear - Here's a remake that might actually be better than the original. Robert DeNiro will scare the hell out of you in this, and is the one horror movie Scorsese made.
Other non-mob movies worth checking out: Alice Don't Live Here No More, Raging Bull, and Hugo.
Scorsese has always said that growing up he had 2 things he was most interested in: Orthodox Christian theology and Rock music. You will find both things sprinkled heavily in his films with religious imagery and blaring classic rock songs. There's a hilarious part in Mean Streets about a preacher that I won't spoil cause it has to be seen to be believed. His use of rock music needs no introduction if you've seen his movies. He's the guy who sets a gunfight shootout in Casino to Cream's instrumental jam Toad.