I think that there can be different understandings of critical or "main" features in Romantic poetry. I think that one main feature of Romantic poetry is the emphasis on self. There is a primacy that Romantic poetry places on the experience of the individual. The subjective experience is something that strikes at the very heart of Romantic poetry. This subjective experience is something that distinguishes Romantic poetry from other forms of the discourse in the role it plays in praising in the individual and their own perception of the world.
As the subjective experience is one of the main features of Romanticism, I believe that the emotive exploration of this condition is another main feature of Romanticism. The praising of emotions and the affect of the individual is a significant part within Romantic poetry. The emotive condition of being in the world is something that animated much of Romantic poetry. In contrast to the scientific and detached claims of the Enlightenment, subjective emotions became praised within the poetry of the Romantic thinkers. In this, the exploration of emotions becomes a significant part of Romantic poetry.