It's interesting that you picked up on this because I'd agree that the NEP period is often overlooked in the histories of the early Soviet state. Much like the contemporary Weimar Republic, there's a temptation to read the NEP as either merely the aftermath of revolution or a foreword to the transformation 1930s. This understandable: 1917 was a world historical event of major importance, while the foundations of the enduring Soviet system were laid during Stalin's revolution.

The NEP has therefore often been seen as an odd interregnum. With the exception of the 1980s (when Bukharin was briefly popular with American academics and reforming Soviet politicians), the NEP has been traditionally overshadowed in the historiography by the October Revolution and Stalinism. In Shelia Fitzpatrick's Russian Revolution, for example, the short chapter on the NEP consists almost entirely of the intra-party disputes over the succession struggle and economic course.

On the one hand I don't think this does the years in question justice. This was an exciting half decade, one that witnessed a rich debate as people tried to understand just what a new socialist society was supposed to look like. Passing over the big political items, conversations also abounded on a wide variety of topics: education, rapprochement with the intelligentsia, peasant policy, new scientific discoveries, attitudes towards religion, relationship with the working class, healthcare, sexuality, etc, etc. These were all up for discussion, albeit within set limits.

And it's particularly worth nothing the cultural and intellectual flowering of the decade. One just has to look at a small sample of the names publishing/working during the period: Eisenstein, Ilf and Petrov, Mayakovsky, Sholokhov, Bulgakov, Gladkov, Mandelstam, Babel, etc. Not all of these were exclusive to the NEP and there were limits to what the censor would allow (eg Zamyatin's We), but this was still a vibrant cultural milieu, easily the most expressive in the history of the Soviet state.

But there's a reason that this is largely overshadowed: the NEP came to an end. In pretty much all of the fields noted above, the 'Great Turn' of 1928 heralded a decisive break with the past. A decade later the country was being run by a very different cohort and along very different lines. Any of the ambiguities of the NEP had been erased in the white heat the Stalin industrialisation drive.

So when we step back what, aside from a wealth of cultural riches soon to be condemned, was actually the long-term impact of the NEP? And here we see why people tend to gloss over the 1920s.

At a high level, the NEP saw the Soviet regime finally establish itself. On the economic front - always central to early Soviet history - what had begun as a set of stability measures quickly paid off. The agricultural and industrial recovery was relatively swift and by 1926 the economy was returning to 1913 levels of production (albeit with new structural constraints). The urban working class slowly reconstructed itself and for the first time the Party began to made inroads into the countryside (significantly aided by the demobilisation of the Red Army). It was also a period of relative calm in foreign affairs.

But if the NEP was a chance to recover (successfully) from the Civil War, it was also laying the foundations for its own demise. Whether one accepts that there was a genuine potential for an alternative path in the 1920s (eg Cohen) or that this was merely a breathing space for the inevitable industrialisation drive (eg Carr), Stalin's 'revolution from above' would not have been possible without the NEP. The perceived retreat from socialism, yearning for a return to the 'heroic period' of the Civil War and scourge of mass unemployment all made a renewed socialist offensive attractive. Yet much of the thinking, practice (eg the 'regime of economy') and institutions (particularly TsKK-RKI) of the Five Year Plans were also developed during the NEP. And, of course, these years were formative for the later Stalin generation of leaders that would govern the USSR up to the 1980s.

So the Party emerged from the NEP a much less pluralistic organisation but also with the strength to enforce policies (eg collectivisation) that would have been unthinkable a decade earlier. Paradoxically this was the product of one of the freest and intellectually challenging periods of the Soviet experiment.

Recommended Reading

As I said, the NEP is relatively neglected in the literature, at least when compared to the forests that have been expended on 1917 and Stalinism. Lewis Siegelbaum's Soviet State and Society Between Revolutions is the best place to start, particularly because it has the great benefit of treating the period on its own merits. Ditto with Shelia Fitzpatrick et al's Russia in the Era of NEP, although, like the rest of that particular series, this collection of essays goes too far in avoiding the political dimension.

Other key works would include Stephen Cohen's Bukharin, nominally a biography of one of the major players of the period. It's a bit outdated - and very much cheerleads Bukharin as a viable alternative to Stalin - but still the best narrative of the political and economic disputes that wracked the Party leadership. The usual counterpoint is EH Carr, whose multiple volumes on the period (in Socialism in One Country and Foundations of a Planned Economy) treat the NEP as a staging point en route to the inevitable crash industrialisation of the 1930s. Not for those who can't stand detail.

Finally, I didn't spend time on this above but Kevin Murphy's Revolution and Counterrevolution has a good couple of chapters on how NEP institutions enjoyed legitimacy with the working class at shop floor level. Bodies like the trade unions and Rates Conflict Commission, (RKK) allowed workers input into management decisions in a way entirely unlike previous or later experiences. This touches on the broader question of how the NEP was discarded for the more coercive Stalinist system.