There are some metrics which may help a naive assessment.
The Economist's Democracy Index ranks nations on a scale from 0 to 10.
0-4 Authoritarian Regime, 4-6 Hybrid Regime, 6-8 Flawed Democracy, and 8-10 Full Democracy.
Between 2006 and 2017 Venezuela fell from 5.42 to 3.87, making it an authoritarian regime.
The Economist's Intelligence Unit explain their methodology, which takes into account measures of "free and fair competitive elections", "civil liberties", "functioning of government", and "political culture".
Freedom House's Freedom in the World 2018 report classifies nations on a scale of "free", "partly free", and "not free", finding Venezuela not free. Their methodology is based on how national realities compare with the the UN's 1948 Universal Declaration of Human Rights.
Reporters Without Borders' 2018 World Press Freedom Index ranks Venezuela 143rd out of 180 countries, with a score of 46.03. They score nations from 0 to 100 (best to worst). RWB methodology calculates press freedom based on questions of "pluralism", "media independence", "environment and self-censorship", "legislative framework", "transparency", "infrastructure", and "abuses".
In 2017 they described Venezuela as being "ever more authoritarian":
Nicolás Maduro does his utmost to silence independent media outlets
and keep news coverage under constant control. The climate for
journalists has been extremely tense since the onset of a political
and economic crisis in 2016, and is exacerbated by Maduro’s frequent
references to the “media war” being waged by national and
international media outlets to discredit his administration. Arbitrary
arrests and violence against reporters by the police and intelligence
services reached a record level in 2017. Foreign journalists are often
From these measures we can conclude that Venezuela has become an increasingly authoritarian society. This has been driven in no small part due to the leadership of presidents Chavez and then Maduro.
Presently Maduro has exhibited many of the characteristics we would think of as quintessentially dictatorial, and has made decisions to empower himself at the expense of the parliament. For example, the 2016 state of emergency, declared by the presidency and supported by the Supreme Court against the will of parliament.
Because the slide into authoritarianism is owing primarily to an overbearing presidency, this can be said to make Venezuela effectively a dictatorship.