Elite and the (shoddy) sequels took many years of (off?) my life. I love Civ and all the spin-offs (alpha centauri etc) those also had me glued to the keyboard.
Recently, Fallout 3 and Borderlands are the ones for me. Both I played beginning to end pretty much non-stop about 2 and half times (once through, through again with different character build and then again with another build that I get bored with).
The all time hat's-off award goes to a D&D campaign I played in for YEARS. All the original Gygax modules (tweaked for players who'd done them before), including 'The Temple of Elemental Evil', another game I've rinsed out totally, all the way from copper-hoarding lowbies to kicking Vecna's (and Iuz') ass. As I said, years of hilarity, action, drama, tragedy and beers with yer mates, awesome.
I still am an active player of Advanced Squad Leader, a tactical WWII board game. A typical game can take 6-8 hours, or more.
Is that an Avalon Hill 'bookcase' game? I have Panzer Leader and Squad Leader, just wondering if they're the same series.
[Edit] Forgot Diablo ][
<facepalm>