What video or arcade games have you invested oodles of time and quarters playing and never finished?

BATTLEZONE

I never finished Final Fantasy 12.

The video games I grew up with weren’t generally designed to be finished. I relate to them as being entertained for a while, rather than as things to try to “finish”. I liked many of them. Particular favorites include:

Venture
Bosconian
Assault
Joust
Defender

My dad and I also agreed the best strategy, was to get into games we could own (so we wouldn’t have to travel to arcades, nor spend quarters for each play!), so on a console or later, computers. I have played literally thousands of computer games. The ones I’ve spent the most time with include:

Atari 2600: Adventure

Intellivision: Space Spartans

Atari 8-bit computers: (all games I’d still happily play)
Necromancer
Star Raiders
Encounter
Joust
War In Russia

Atari ST:
Llamatron 2084
Dungeon Master (well, I did finish 1 & 2 – haven’t finished the 3rd one, which is for MSDOS/Mac/Amiga but sigh not for Atari)

Linux/MSDOS/Windows/Mac: (note only the first two have any way to “finish” them, but I mostly played them multi-player)
Myth: The Fallen Lords
Myth II: Soulblighter
Tigers on the Prowl
Panthers in the Shadows
Dominions 1–5 (by Illwinter)
Conquest of Elysium 3–4 (by Illwinter)
Space Empires IV Gold
Combat Mission 1–3

I’ve always found pinball and computer games boring.

The most time that I spent playing a computer game (came free with my 1998 iFruit computer) is “Nanosaur” (https://www.youtube.com/watch?v=dIHUJ2gKS14). It’s about how humans brought dinosaurs back to life then the dinosaurs took over as humans became extinct. The advanced Nanosaurs needed more dinosaur DNA so they made a time portal to go back in time to the age of dinosaurs to collect fresh dinosaur eggs.
Made it to the final level where lava flows start taking over but never finished it. Played it about a couple dozen times and then got board.