It

It is a 1986 horror novel by American author Stephen King. It was his 22nd book and his 17th novel written under his own name.

Plot
Seven outcasts in Derry, Maine, are about to face their worst nightmare - an ancient, shape-shifting evil that emerges from the sewer every 27 years to prey on the town's children. Banding together over the course of one horrifying summer, the friends must overcome their own personal fears to battle the murderous, bloodthirsty clown known as Pennywise.

Why IT Rocks (No Pun Intended)

 * 1) Well-done character and story development.
 * 2) Very intense and scary moments.
 * 3) * Such as one terrifying part is where Stanley (one of the members of the Loser’s Club) has his first encounter with IT in the synagogue in the form of a hideous, creepy flute playing woman (Judith) that came from a painting in his father’s office.
 * 4) * Another terrifying part is when Henry Bowers kills his father while the woman and children encourage him from the television.
 * 5) * Probably the scariest is in the beginning, where Pennywise bites off Georgie's arm and kills him in the sewer.
 * 6) The Losers Club members are very likable and relatable, as they each have something that makes them victims of bullying, such as race, disability, and parental incest.
 * 7) Most of the other parts are very memorable.
 * 8) * Mainly the unforgettable Pennywise dancing part.
 * 9) Henry Bowers and his gang of bullies are very entertaining and sadistic in their own ways.
 * 10) The ending is heartwarming, cool and emotional all at the same time.
 * 11) A brief but touching story arc about a love triangle around Beverly, Ben, and Bill.
 * 12) The Loser’s Club share a very realistic, loving bond.
 * 13) Earned a tv special and two movies.

Bad Qualities

 * 1) Forgotten plot-holes are here.
 * 2) Even though Pennywise is portrayed perfectly, it seems a little too scary to be viewed as a good convincing clown that could trick its victims with its clownish behavior. Like the part where it meets Georgie. Nobody, especially somebody Georgie's age, would ever be attracted to somebody that scary looking.
 * 3) Mediocre villains, although very entertaining, like the bully, Henry Bowers, and Beverly's father, Alvin Marsh.
 * 4) The fact that the Losers Club literally have an orgy after defeating It is disgusting. The author, Stephen King himself also hates it so much that he regrets putting it in his novel. It was so bad that both of 1990 miniseries and 2017 movie adaptations did not use that scene at all.