Bad ending?......spoilers!

This actually brings up an interesting scenario. What if, instead of Leamas going over the wall first, he had Nan go over first? Smiley and Mundt were taking a rather big gamble on that one. They had kept Nan alive simply to get Leamas back home. Nan was never going to leave East Germany alive, but Leamas would never have left without her, either.

Leamas was finished as an "asset" anyway - and, in his state of disenchantment, a possible liability - so was therefore expendable. This was the tidiest tidy solution for his controllers.

BTW Please can anyone enlighten me on what the guard calls out over the loud-hailer at the end?

Then the movie would not have been faithful to the original novel. The bleak ending was the whole point.

Probably the biggest departure from the book occurs at the end. In the film, the young guide shoots Leamas and Nan, while in the book the the precise origin of the shots is not mentioned.

In the book, there are shots when the searchlight picks up Leamas and Nan at the wall and various orders in German were heard while the shots rang out. I think the intention of the author was to attribute the shots to the border guards, however there is mention of French and English voices as well as German voice while the shots were being fired, which leaves a certain amount of doubt as to who exactly was responsible for the shots. The film is more unequivocal as it clearly shows the young guide firing the shots and the implication is that it was Mundt and hence possibly British intelligence, his pay master, who was behind the shooting.

It's the same way the book ends, which was critically acclaimed, which I suppose includes the ending. Dull? That's what Leamas claims the whole thing is, in his speech to Nan (whose name in the novel, by the way, was Liz Gold, a rather obvious reference to the fact she may be Jewish, like the expendable Fiedler). Chinatown? That came five years later, and is a film noir. Trite platitudes and catchphrases ('The stuff dreams are made of') are a staple of film noir, not spy films based on novels by John LeCarre. Leamas played a worn, embittered, alcoholic agent to carry out Control's plan. The trouble was, Leamas really was a worn, embittered, alcoholic agent, who foolishly found love while on the job, and then let that be the straw that broke his back. He should not have died? Tell that to Control; I'd say Control pretty much got everything he wanted, including the glorious, heroic death of his Man in Berlin, who might otherwise have become unreliable, dangerous, and... who knows? Defected? Knowing how Control turns out in LeCarre's subsequent novels, I would say this story, whether filmed or written, turned out exactly the way it always was going to.