When an epoch ends, the intellectual leaders of the new epoch name the one that just ended (this is a general observation, cf Early modern vs late modern vs post modern?).
E.g., Khrushchev called Stalin's
Brezhnev called Khrushchev years "voluntarism", and Gorbachev called
Brezhnev's years "stagnation" ("застой").
The existential problem of the USSR was its inability to deliver on its
messianic promise of prosperity and happiness, and that required an
explanation, and the easiest was was to blame the past and the surroundings:
- For Stalin it was the "Tzarist heritage" ("тяжёлое наследие царизма" - he could hardly blame Lenin, who, first, was a "saint", and, second, ruled for only a short time) and "capitalist encirclement" ("капиталистическое окружение").
- For Khrushchev - Stalin's excesses and USA meddling ("происки США").
- For Brezhnev - Khrushchev's voluntarism, WW2 devastation and USA meddling.
- For Gorbachev - Brezhnev's stagnation and USA meddling
(notice the common theme).
Were Brezhnev's years truly stagnation?
All attempts of economic reform failed, and the nature of communism took over: bureaucracy appropriating all benefits while bearing no risks.
During Stalin's years, a "failed" (in the eye of his superior, which might or might not correlate with reality) bureaucrat was often executed. When Khrushchev broke this lame "feed back", bureaucrats stopped caring about the outcome.
The army gobbled up all the oil revenues and achieved missile parity with the complacent USA.
Corollary: Space and other military-related research: up
Space industry and research benefited from the arms race.
While losing the Race to the Moon and wasting precious resources on the attempt to duplicated Space Shuttle, USSR still made interesting progress with space stations.
The Khrushchev Thaw was over.
Incidentally, I highly recommend Советская детская литература и её современные перспективы: it is a very incisive (if somewhat controversial) analysis of Soviet culture.
Other research: uppish
With Stalin's fundamentalism
and Lysenkoism gone,
researches were more free to pursue their interests.
E.g., fox domestication!
This was limited by the usual funding shortages (if it's not military, you need connections at the top to get funded).
Since mathematicians do not need much funding, the Soviet school of mathematics blossomed!
PS. One of the immanent aspects of the Soviet life was the alternation
of the leaders: each one was the "antithesis" of the previous one.
This is especially evident in the hairdo: Lenin, Khrushchev, Gorbachev
and Putin are bald; Stalin, Brezhnev, and Yeltsin are not.
Even the non-entity Medvedev fits the pattern!