Blah blah blah, not true to the original Doom, blah blah blah, it sucks, tries to hard to be horror, blaaaah...
Think what you want. I personally found Doom 3 to be very fun. Sure, the weapons don't feel as kickass as they did in the original Doom and the multiplayer is a complete joke, but it's still fun.
It's basically a retelling of the original Doom, where experiments with teleporters go screwy and open portals to Hell.
Doom 3: Phobos is a mod currently in development, with a much better shotgun model and modified gun damages that will hopefully not suck as much. They have an Arachnotron, too.
Open Co-Op is another mod, it adds a co-op mode with support for custom maps and Resurrection of Evil.
Resurrection of Evil is the expansion. It takes place two years after Doom 3 (2147), so you play as a different marine. It adds 3 new weapons: The Double-Barrelled Shotgun, the Ion Grabber (think Gravity Gun, but you can only hold stuff for 4 seconds), and the Artifact. It also adds a few new enemies.
The BFG9000 acts more like Quake II's, but slightly weaker. I'd prefer it a little stronger, but it works.
