There's nothing inherently wrong with ninety minutes of dialogue, as long as what's being said is worth hearing. That's not the case here. The only ones who appreciate what these people have to say are the characters themselves. Except for the exchanges between Marty and his girlfriend, it's difficult to find high points. It's never clear where Marty Fine is going, or whether it ever gets there.
Transitions are virtually nonexistent, and the ending is abrupt.
I have little doubt that Marty Fine is destined for obscurity.