The chief characteristic about Hardy's style of characterization, which includes informing the reader of his opinions regarding the characters, is that of direct commentary about psychological and emotional states of the characters. This is significant since Hardy followed the school of Realism introduced by Balzac in France around 1840. Realism grew following the publications of Balzac's Human Comedy beginning in 1829 and ending in 1837. This kind of detailed narrator commentary was earlier predicted by Hawthorne's style of characterization in America with his works published beginning in 1828.
An example of Hardy's approach to this is clearly set out in his introduction of Tess in Chapter II of Tess of the d' Urbervilles. When we meet her, her description is superimposed over the information we get in Chapter I that she is the daughter of the last of the noble d'Urberville line of Norman descent having come to England with the Norman Conquest. We learn that she has noble impulses and is given to anger and shame for unjust and ignoble causes, respectively.
"Look here; I won't walk another inch with you, if you say any jokes about him!" Tess cried, and the colour upon her cheeks spread over her face and neck. In a moment her eyes grew moist, and her glance drooped to the ground.
With this passage, Hardy lays bare her deepest psychological impulses, those of righteous indignation and shame for her family's and her own folly. These same impulses will guide and prompt her throughout the story. We also learn she is young and without experience to temper her emotions. This lack of experience is probably the central factor leading to her tragedy. We also learn that Tess is a commanding and upright young lady who gives her slightly wayward parents a well-deserved reproach with the flash of an eye and an example set by her own exemplary behavior:
and hardly was a reproachful flash from Tess's dark eyes needed to make her father and mother rise from their seats, hastily finish their ale, and descend the stairs behind her,...
So, the dominant means that Hardy uses to inform the reader of his opinions regarding the characters, as exemplified by his introduction of Tess, is to comment upon the character's internal struggles and conflicts with psychological motives and forces, thoughts, emotions and understanding. It is through these means also that Hardy proves his thesis that the story of Tess is the story of A Pure Woman (the subtitle) because this characterization technique within Realism shows her inner psychology that stands true despite external circumstances.