What would America be like if the Left had total control?
The answer depends, I suppose, on who and how vociferously people bitched about the lifestyle they enjoy as a result of the policies the left implements. The short answer is that some sort of major legislation/initiative would get passed, which is a good thing in my mind because like it or not, when something major gets done, we at least have the opportunity to learn from it, correct what's wrong with it, and build upon it. Even making a mistake is better than doing nothing.
The Right has had complete control of the presidency and Congress since January and thus far not one major piece of legislation has been enacted, not even the "easy" stuff. Hell, the easiest things to do because presidential fiat is all it takes to do them -- implement import tariffs and cancel NAFTA -- still haven't happened. (I don't think they should, but whether I think they should isn't what was asked about.)
The Left held sway during the Roosevelt years, and FDR got elected four times, after all, and that never happened prior to FDR and he was the only POTUS to have served more than two terms. People must have been pretty happy with his and the Left's policies for that to have happened. Back then, people seemed quite happy with government acting as their "savior" and that's about what Trumpkins are expecting of the government under Trump.
It stands to reason, therefore, that neither the Left nor Right has a lock on the notion of the government being the solution to all that ails us as a nation. In light of that, I doubt that it matters much whether the Left or Right has total control. The fact is that whichever party coddles the polity will be lionized.