That could be because the Doom series was never meant to be multiplayer, the first Doom had a multiplayer option, yes, but it was mainly co-operative play or a limited deathmatch. Half life was meant for Multiplayer, but multiplayer doesn't make the game, if that were true then Return to Castle Wolfenstein: Enemy Territory would logically be the best game in the world along with all MMORPGs, seeing as it's totally multiplayer.
Storyline is essential to me in games too, truth be told, Doom 3 doesn't have much of a storyline: Battle undead hell spawn to find a way to close the gate to hell to save earth. Granted, no much of a plot, but at least it HAS a storyline. All Half Life 2 seems to be is a long string of meaningless missions, carelessly thrown together in a string that's supposed to flow like a story. :rolleyes: