1) JeanP is right; as the photo I reproduced suggests, the lines are caused by shortages of even basic goods for the same reasons as they were in the Eastern Bloc.
2) jsonitsac also has it right; Venezuela ranks 181st out of 189 in national rankings of ease of doing business, 176th out of 178 in the Index of Economic Freedom and 164th out of 178 in Transparency International's Corruption Perceptions Index; it is not tempting territory for any corporation. The assets of the oil corporations were expropriated in 2007 and the state oil company, PDVSA, is run entirely by and for government supporters.
Oil prices are still higher than they were in 2010. The drop in price is not the product of theories worthy of CSTDT, but of a drop in demand, particularly in China and Europe where the economy has become more sluggish than before. If anything, the drop in price has hurt smaller producers in the US and production through fracking by US companies, all of which relies on traditional sources from OPEC countries, including Venezuela and Saudi Arabia, being much less cheap and plentiful than they are now.
As for the opposition in Venezuela being "mostly middle and upper class," this should come as a welcome surprise to the 80% of Venezuelans who currently disapprove of Maduro's record; they never realized that the frustrations you feel standing in line for hours waiting for milk made you upper class.
And the opposition mostly financed by the US? That will come as a shock to the large contingent of former PSUV members discarded by the party at one stage or another. There is funding from US organizations, sure, just as there is in any country where it's difficult or dangerous being a democratic politician. In most transitional democracies, like the former communist countries, money from George Soros and the like is welcome; it's countries like Iran and Venezuela who would rather that the government's control of the courts and patronage weren't challenged.
Carlos Andrés Pérez could make anyone look good. However, he didn't out-Reagan Reagan in firing union members, didn't threaten Venezuela's neighbors from Colombia to Barbados, didn't have the world's second worst homicide rate and there was food on the table. No longer, alas.