A great, gripping action tale. The opening sequence of Plissken's robbery I think was unnecessary - we see too much of the outside world - and I think was good they cut. We plunge into the exciting drama of the president's plane going down, trying to get him, being knocked back, asking for Plissken's help, throwing Plissken in.
Once he arrives in New York things get, perhaps inevitably, more episodic - going to the theatre, meeting cabbie, tracking down Brain, being captured, meeting the Duke, engaging in the fight, the final run for safety. The ending is effective.
The "world" of New York prison probably could have been explored more - it would make a great setting for a TV show.