This is such a big discussion but in my opinion Snape as a person is a bad guy, look at the way he behaves (not necessarily towards Harry but also towards Hermione and Neville...) and his obsession with Lily in my opinion is very exaggerated, it is true that he is on the "good" side but as a person I personally would not want him close to me It's not that I'm not aware of the good things about him, but the bad things (the obsession with Lily, the attraction to Voldemort and especially to Opal, the disgusting behavior to the students, etc., etc.) far outnumber the (really) good things (he is undoubtedly one of the bravest of the series).