Trotsky was, in Lenin's final written words (which you'll have to look up when Marxists.org is back up), was a great and able theorist. Stalin had collected power in his hands.
Trotsky was fundamentally correct about his analysis. Even Stalinists, who tend to despise Trotsky, eventually end up getting back to his analysis of a given situation. For instance, Stalinists (as Stalin himself) don't really stick with the counter-industrial scheme, the Third Period nonsense, or advocate helping Kang Khi Shek instead of Mao, or any other damned thing.
However, before this turns to any kind of gloating one way or the other, Stalin had the power in his hands. In the Marxist vernacular, this has to do with praxis. But for here, we can simply say that Trotsky's theories, like all theories, are useless should they not be implemented.
Philosophers have merely interpreted the world in various ways; the point is to change it..
The other thing here is that one must be aware that Trotskyists, today, tend to be of the two camps that Trotsky repeatedly told everyone to resist:
Trotsky wrote:There is no doubt that the USSR today bears very little resemblance to that type of Soviet republic that Lenin depicted in 1917 (no permanent bureaucracy or permanent army, the right of recalling all elected officials at any time and the active control over them by the masses “regardless of who the individual may be,” etc.). The domination of the bureaucracy over the country, as well as Stalin’s domination over the bureaucracy, have well-nigh attained their absolute consummation. But what conclusions would follow from this? There are some who say that since the actual state that has emerged from the proletarian revolution does not correspond to ideal a priori norms, therefore they turn their backs on it. This is political snobbery, common to pacifist-democratic, libertarian, anarcho-syndicalist and, generally, ultraleft circles of petty-bourgeois intelligentsia. There are others who say that since this state has emerged from the proletarian revolution, therefore every criticism of it is sacrilege and counterrevolution. That is the voice of hypocrisy behind which lurk most often the immediate material interests of certain groups among this very same petty-bourgeois intelligentsia or among the workers’ bureaucracy. These two types – the political snob and the political hypocrite – are readily interchangeable, depending upon personal circumstances. Let us pass them both by.
Nonetheless, Trotsky becomes a flag under which both, "the political snob," and, "the political hypocrite," can rally as he isn't Stalin. In this vein, most Marxists today consider themselves Trotskyists whether they are or not. Some tendencies, like those that follow Alex Callinicos, claim to be Trotskyists by virtue of them rejecting Trotsky's views and thus saving Trotsky from himself—as if the memory of a fallen saint is more important than what the saint thought or stood for.
And, as noted, Stalinists can use the same Trotsky flag to shake their fist at while eventually coming to accept the theories that Trotsky laid out in opposition.
As to the capitalist west, you can follow with ease Churchill or the
New York Times, or any other source condemning Trotsky as the worst devil that had ever existed and cheering on Stalin through the struggle—the general assumption being that Trotsky would win. Up until, of course, Trotsky is killed. Then he becomes the ultimate martyr to show the brutality of the Soviet system the sweet prince had naively attended to build before it turned against him as it will turn against everyone that advocates the left. This is, on its face, propaganda and nothing more.
And this is where it gets real hairy as Trotsky is a symbol, more than anything to most people.
It's best to read Trotsky and not trust anything anyone says about him. Not even me.
Alis Volat Propriis; Tiocfaidh ár lá; Proletarier Aller Länder, Vereinigt Euch!