Yeah, definitely Up. :D I went with a friend who didn't know anything about the movie - I had at least heard that the opening had made the critics cry. We were blubbering messes two minutes in. XD Prince of Egypt also is simply an epic masterpiece start to finish.
In the same vain, the beginning of The Lion King also grabs the viewer instantly. So good!

Mad Max Fury Road. The style. The action. The WTF.

Baby Driver, perfect meld of music, editing, and action. Gets me pumped every time.

Recently, Netflix's One Piece had the perfect opening to keep viewers glued to the screen.

Books, The Martian sure as hell knows how to get your attention. XD Yes, Mark, you're indeed quite fucked.
Pride & Prejudice is iconic for a reason.

Also, Lindsay Ellis' first Omegaverse Lawsuit video starts with a banger. XD Reading choice bits of the book this is all about definitely sets the mood. XD