Snape is neither unequivocally good nor bad, and that is what makes him interesting: an analysis
Fan conversations about Severus Snape in the Harry Potter series are very polarized. There are fans who are very sympathetic towards him and others fans who think he is the worst, to put it in simplified terms. I can’t help to think both of these stark sets of opinions are wrong and I really wish fans were more willing to analyze Snape’s role in the overall story (rather than just his individual actions) and what they mean thematically and symbolically. So here we go…
We’re supposed to draw specific parallels between Harry, Snape, and Voldemort. In Deathly Hallows, Harry specifically refers to the three of them as the lost boys of Hogwarts. They all are (1) half-blood wizards with (2) not-so-great home lives (3) who have some particular magical talents (4) who find a place and home at Hogwarts.
Now the connections and similarities between Harry and Tom Riddle have been pointed out explicitly since at least Chamber of Secrets. However, this is also the book where Dumbledore tells us that it is our choices, far more than our abilities, that determine who we are. Snape fitting into the comparison with Harry and Voldemort is only uncovered in the last book, when his full backstory is revealed. Because there is so much going on in that book, including just what’s going on with Snape, this nuance gets overlooked in the analysis of the Harry Potter saga.