It's a subject of some debate, naturally, because it's not as though Stalin or his successors ever abandoned the premise of Marxism. Even among the communist community there's still a few Stalinists mucking about, but the consensus is relatively strong.

On a fundamental governing level, the 'dictatorship of the proletariat' was a dictatorship, certainly, but not the intended kind. This article makes an interesting point about the political statement intended by abstention under a one-party system.

On the economic front, the workers generally did not control the means of production. Legal private enterprise was confined to small-scale agricultural production. In other words, the fruits of labor were unrealized by citizens of the USSR in any form. Soviet land reform, defined by the Decree on Land ended true ownership of the land, but left de facto ownership of the land to those who cultivated it. This was closer to a truly Marxist policy because it ended the sort of absentee ownership that had defined Russian land since the Stolypin reforms. However, control of local resources belonged to the central government and not any ad hoc or legal community.

From year to year and regime to regime we could dally about what was more or less Marxist, but the essential character of Soviet policy was to remove real economic and political impetus from the proletariat in every way.

"... some of the ideas of the communist manifesto in the soviet union"

Do remember that The Communist Manifesto is written almost 20 years before Capital, which is the more developed text. If we're talking about Marx and his ideas, it is from Capital that Lenin and other Russian socialists and communists would have studied his ideas mainly.

Also, your questions could also be phrased as "What is the difference between orthodox Marxism and Leninism?", although your question of course has a practical side to it as well ("how much did they achieve?").

One thing I'm curious about is how the word "dictatorship" was used in the 19th century, since our 20th century history sure has coloured the word for us. Marx thought the Paris Commune to be an example of the dictatorship of the proletariat, and the commune was democratic. A bit later, Lenin had a different view of dicatorship through his idea about the vanguard. If there is any lurking linguist here, what would be the general understanding of the word "dictatorship" in Europe at the time?

Richard Wolff talks about the Soviet Union and what they did and didn't implement, from a Marxist perspective, in this video. So if you want an intra-theoretical view on it, you might find it here even though it is the last lecture of four:

https://www.youtube.com/watch?v=Fgkzhq3-vlA&index=36&list=UUB-5u8VgFc_TI1aAj8_SmDA