It's a different kind of scary. The restraints come down tightly to you (flush with your torso) so you won't be going anywhere.
Splash Mountain's drop is at a 45 degree angle. The biggest drop on Mummy is 50 degrees, which makes it a steeper/scarier drop. It's probably easier to compare to Space Mountain, since that is also an indoor coaster in the dark. As for POTC, I don't know how big their drop is, but Mummy's = bigger. Backwards, you fall about 12 feet.
There's really no stomach drop, but it varies per person I would guess...
Visual effects:
1st scene: mummified/dead bodies all over the place. A shadow that can't be described. A shaking mummified guy that is still alive, only to be killed by the mummy (who breaks out of his coffin). The mummy, Imhotep, sucks out the other guy's soul, so it's not gory.
2nd scene: Imhotep appears on a screen and offers you riches if you serve him (bright light & treasure) or death if you refuse (darkness and 6 warrior mummies appear from nowhere, poised to attack from the side). Plus a falling wall.
3rd scene: flesh eating scarabs swarm around your railcar.
4th scene: Imhotep appears again and mocks you. You then launch quickly into his mouth and he "swallows you".
5th scene: high speed rollercoaster in total darkness. Warrior mummies/ghouls appear and disappear, trying to attack your railcar.
6th scene: Imhotep kills another person (non-gory soul removal), breaks glass & makes the "shards" (water) hit you. He mocks you, then sets the roof on fire.
7th scene: Imhotep tries to catch you again in the same manner of the previous ghouls. A giant symbol appears with a bright light. Brendan Fraser welcomes you back on a screen, then gets attacked by a mummy.