Q: What is a good opposite of pretentious?
The dictionary definition is:
"Attempting to impress by affecting greater importance or merit than is actually possessed."
To which I can think of:
Humility: "The quality of having a modest or low view of one's importance."
Honest/Sincere/Genuine/Truthful: "Free of deceit; truthful and sincere.", "Free from pretence or deceit; proceeding from genuine feelings.", "Truly what something is said to be; authentic.", "of undisputed origin and not a copy; genuine.", "Telling or expressing the truth; honest."
Unassuming: "Not pretentious or arrogant; modest."
Perhaps instead a short phrase like, "Humble and Honest".
However for the commonly understood or vernacular definition, which seems to have a significantly different meaning, perhaps a good opposite would be:
Artless: Without effort or pretentiousness; natural and simple.
Although it's unfortunate that "artless" is defined as being "natural".
An example: "I couldn't follow the film, I found it pretentious.", the opposite could be "The film lacked nuance and was refreshingly ..."