The Abyss (1989)

In James Cameron's landmark science-fiction adventure film:

• the startling, opening credit-less title sequence in which the words "THE ABYSS" emerged from the darkness, and then the camera descended down into the letter "Y" into the ocean - and a view of an American ballistic nuclear submarine, the Montana, that was soon ambushed and sank in deep Caribbean Sea waters (submerged about 25,000 feet down) after encountering an alien species
• the frighteningly realistic nuclear submarine drowning scene, and later the scene of divers surveying the drowned corpses - with expressions that mocked death; also Lindsey's (Mary Elizabeth Mastrantonio) heartfelt and reassuring messages to her estranged husband Virgil "Bud" Brigman (Ed Harris), relayed to him as he descended dangerously into a deep ocean trench to disarm a nuclear warhead
• the many computer-generated images of the watery aliens, including the revelatory emergence of a glowing purple/pink ship in front of Lindsey -- and her later description of it to "Bud": ("It... it was like a dance of light!")
• the amazing "pseudopod" sequence featuring a CGI water-based tentacle that morphed into the faces of Lindsey and Bud
• the scene-stealing, paranoid character of Lt. Coffey (Michael Biehn) -- driven insane by pressure sickness, and his two major tense, action sequences in which he knife-fought with Bud and the "chase" scene with two submersibles which culminated in Bud and Lindsey being stranded in a leaking submersible with only one aqualung

Near Drowning Death of Lindsey

• the subsequent drowning of Lindsey, and Bud's frantic resuscitation scene, using a combination of methods: heart-shocks, pounding on her chest, screaming at her, slapping her, crying, and CPR mouth-to-mouth resuscitation, until she gasped and took a breath: ("No! No, she has a strong heart! She wants to LIVE! C'mon, Linds! C'mon baby! Zap her again! Do it!... Do it!... Come on baby, come on baby!... Come on, breathe baby. Goddamn it, BREATHE! Goddamn it, you bitch, you never backed away from anything in your life! Now fight! Fight! Fight! Right now! Do it! FIGHT, GODDAMN IT! FIGHT! FIGHT! Fiiiiiiiiiiight! Fiiiiiiiiiiight! That's it, that's it, Lindsey. That's it, Linds, you can do it. That's it, Linds, come back, baby. Come on. You can do it, baby"), paralleled by Lindsay's speech to Bud when he descended into the 2.5 mile deep Abyssal Trench to defuse a nuclear bomb: ("I'm with you. I'll always be with you")
• Bud's encounter with the angelic-looking NTI's (Non-Terrestrial Intelligences) and his being taken to their awe-inspiring underwater city in a 2001-ish sequence
• the astonishing deleted "tidal wave" sequence (restored in the director's cut) in which both coasts were threatened by massive amounts of water - but then subsided (but with a warning from the aliens to Bud and all of humanity against war-like aggression)
• the scene of the final kiss between Bud and Lindsey: ("Hello, Brigman," "Hello, Mrs. Brigman")