How successful were Mussolini's policies before he was evicted from office? Is it fair to say that the onset of WW2 prevented any long term success?

Fascism did not walk into WW2 the way one walks into a rake. It was not really an accident that could be disconnected from the combined policies that led to it.

By the late 1930s Mussolini was certain that the Italian participation to a general conflict was going to be a key moment in the success of fascism. And in fact, while it is difficult to keep track of all the moments, instances and interests that created the conditions for the eventual Italian entrance into the conflict, those very moments serve as evidence that the Fascist Regime sought in the War not only an ideological confirmation but also the solution of problems it could not solve within itself.

Many of the steps – even the most bizarre ones, like the campaign against an excessive consumption of pasta or the abolition of the formal "third person" lei - taken in the years leading to the War find their necessary context in an effort to achieve an actual and lasting fascistization of the Italian society. Something that many fascist leaders had begun to see as severely lacking, both in the attitude and national morale.

While the Ethiopian conquest (with the following proclamation of the Empire) had brought a superficial enthusiasm and a bout of generic consensus towards the Regime, it was a fact that the costs, military and economic alike (the Italian gold reserves were in 1939 depleted to a fraction of what they had been in 1919), had not been rewarded with that cultural and social renovation that, even in its empty rhetoric, a part of the Regime genuinely strove towards.

Mussolini was growing increasingly impatient with the Italians – a fact mirrored by his short temper and parallel indifference towards his closer collaborators and the various administrative matters; Roberto Farinacci had reported with concern over the behavior of the Italians in the newly conquered Ethiopian region, stressing the need to keep them apart from the locals; Giuseppe Bottai was busy with the task of creating the new Fascist Italian, with his Ministry of National Education. An attempt that Bottai – who, far from changing his mind entirely on the fascist experience, would later reclaim the value of what fascism had tried to be – would soon declare a failure; acknowledging how much the Regime had proven unable to appeal to the new generations and finding an odd path to personal atonement in asking leave to join the French Foreign Legion in 1944.

Even the somewhat positive results obtained by the Regime with the creation of the IRI in 1933 to contrast the effects of the economical crisis led to a deeper entanglement of the strategic industrial sector (steel, energy, chemistry, weapons) and the state finances; in a way connecting ever more strongly those branches of the industrial world that were more prone to military adventurism and the state apparatus.

In the cultural landscape, it is well known that the Racial Laws of 1938 led to various notable personality being forced out of their position or just leaving the nation as a sign of disagreement with the Regime. But already during the previous years Fascism had sacrificed any residual cultural vivacity in favor of a progressive homogeneity that resembled more and more stagnation.

There are many details that one could add here – and in fact this answer could probably take the space of a few books – but I have chosen to give the very quick version. Feel free to ask for clarification on a few points, of course.