Just done a scene-by-scene comparison with the movies

1990/2017 Photo album + Slide projector

Signs of the times, but whilst Pennywise can intimidate the Losers through the photo album verbally and only stick his hand towards them, with the slider projector he can scare them with the malfunctioning projector, and then scare the crap out of them in person by chasing after them in giant form.

WINNER: 2017

1990/2017 Children in sewer

In 1990, very little happens, such as Stanley being singled out for eating by Pennywise, Eddie and Bev coming to his aid with an inhaler and silver pieces, but then when Pennywise is injured, flies over them and goes into the sewer in the worst special FX ever seen on TV. In 2017, he paralyses Bev with the Deadlights, attempts to lower Bill's guard by pretending to be Georgie, and launches a sustained shape-shifting fight against all the Losers, even managing to take one of them hostage. But it's all for nought as the Losers, angry and pissed off beyond reason, take down the clown for the next 27 years.

1990/2019 Adults in sewer

In 1990, the Losers enter IT's lair through a cheesy little wooden door surrounded by skulls (Fee Fi Fo Fum, indeed). Then it's off to rescue Audra in the webbing until cheesy and awfully-animated spider-like creature (which is not even like a black widow or anything scarier) approaches them. Then it reveals the Deadlights through it's underbelly (WTF?) which incapacitates some of them, and Eddie is crushed in the midrib to death after doing his inhaler trick whilst Bev shoots the underbelly and IT scurries off, and they eventually rip it to pieces and leave the heart they pulled out close to the body. Then it's off to bring Audra back from a catatonic state (who cares?)

In 2019, it's a lot more epic, with Pennywise putting all of the Losers through the wringer, and "testing" them in his own way, and after Deadlighting Richie and stabbing Eddie fatally, the Losers realise that they need to make him smaller, and so they tell him what he's done, basically, and he shrinks enough so that they can pull out his beating heart and crush it. Then they escape the collapsing sewer, wash, reminisce, and eventually go their own separate ways. Finally, they remember their childhoods and their friendships, and Mike leaves his "prison where IT showed him what IT wanted him to see" in Derry and that's a nice ending.

At this time, a comparison shouldn't be necessary, but DAMN, is it NEEDED.