What are the basic features of these three eras in literature: The Neo-Classical era, the Romantic era and the Victorian era?
In the Neo-Classical era, there were set rules that people of that age worked according to and there was no freedom of self expression. The Romantic period was a period of rebellion, independence and freedom. The writers of Romantic age rebelled against the Neo-Classical age while in the Victorian age, there was a period of both Neo-Classical and Romantic age.
You are correct that the Romantic era was about freedom of thought and expression. I would add that it is often also associated with a heavy emphasis on nature. As industrialization was just beginning and people were flocking to crowded cities, many of the Romantic poets and writers wanted to highlight the dangers of industrialization or chose to write about the beauty of restoration through nature. Think of William Wordsworth, who used stream of conscious to communicate how humans become whole when they are surrounded by nature, and William Blake, who wrote about loss of innocence for those living in the city ("The Chimney Sweeper" from Songs of Innocence and Experience). When you think of Romantic literature, think of overly emotional writing with a strong emphasis on the self and nature.
Victorian literature is a lot like Victorian architecture: overly detailed, decorative, lots of embellishments. Think of novels like Vanity Fair and poets like Alfred Lord Tennyson. During the Victorian era, writers were focusing a lot on different social classes and the struggle to climb social ranks. They were also focusing a lot on women and their roles in society, since they were suddenly beginning to change a bit. There was a large emphasis on scientific developments during this time and people (and writers) were coping with these new ways of viewing their roles in the world and the universe. For this reason, many writers tried to reach back and pay homage to older styles of writing as an attempt to go back to a simpler time. When you think of the Victorian writers, think of very wordy, lengthy, descriptive sentences with a strong emphasis on details.
The Neo-Classical era was a time when writers focused mostly on recreating the classical of the past. Emphasis was on such things as man and religion or man and harmony or heroism. Think of Alexander Pope and John Milton.