id clearly and deliberatly slowed the pace with DOOM3.
Seems to me it also divided the action/shooter camps in half. Namely:
1) Those that enjoyed the game and took it for what it was - a glossy retelling of a story that was previously only implied. These guys were happy to trawl the base reading PDA's and finding keycards to open ammo lockers etc.,
and 2) those that just wanted the DOOM action of old. ie. You, your shotgun and a room full of hell
Personally I fall in to the latter so for me the game failed to meet my expectations.
But that's my opinion. Certainly doesn't mean it has to be everybody elses.
The only comparison with Half Life 2 is the 3D presentation of the game. Oh and stuff gets shot, too.