If Scorsese were offered an opportunity to re-do some of the scenes in "Mean Streets", I bet he would take it and try to fix some of the hurried, under-directed, and over-improvised spots. This low-budget picture was made in 1973, three years before "Taxi Driver", when Scorsese was not "bankable" enough to ask for an adequate budget to do it right. The reality of commerce in film industry often manifests prominently in low-budget movies, in which the filmmakers are forced to do fewer takes, fewer camera setups, fewer everything. This is, of course, not to say that high-budget movies are automatically better.
"Mean Streets" depends heavily on the charisma of a newcomer (at the time) named Robert De Niro, who is not the lead, whereas Harvey Keitel is, but the latter is stiff and uneven throughout the movie, so De Niro basically steals the show. The premise of "Mean Streets" has to do with a bunch of swaggering young Mafia-wannabes trying to maintain an uneasy relationship with the older and more established mobsters. Scorsese knows the neighborhood, the Little Italy section of New York, well enough to go deep into the collective psyche and is courageous to show us some of the ugly aspects of the ethnic enclave.
The way Scorsese uses music as a "needle" to thread the seemingly chaotic scenes together in "Mean Streets" is a worthy case study for the students of the semiology of cinema.