Doom 3: Resurrection of Evil doesn't fix the flashlight or the multiplayer issues, but everything else has been refined to make this trip to hell the penultimate Doom 3 experience the original game should have been.
Less repetitive environments. More shootouts. Awesome, fun-to-use new powers to help you through said shootouts. More than its source material, this expansion refines everything great about Doom 3 into 6-10 hours of pure shooting joy. This isn't impressive when compared with the original's lengthy 20 hour + campaign, but 1) this is an expansion pack, and 2) in hindsight, Doom 3 could have benefited from a little more game being left on the cutting room floor.
Case in point: Whereas Doom 3 really starts to drag in many areas; Resurrection of Evil never misses so much as a beat. Besides the tweaks made to the length, the two new weapons (no, the grabber gun is not just a HL2 ripoff – boss fights use it quite creatively) and the bullet-time powers give Doom some much-needed depth without straying from what made it a hit in the first place.
The first game had a better story (really, it was good!) and the multiplayer still – in a word – sucks, but for an 21st century single-player Doomathon, Resurrection of Evil is the game most of us wanted in the first place, and that's why it scores higher than the original.
-George