To make short answers of those questions: a little, no, depends on your idea of "worth."
Halo 3 ODST has you filling the shoes of "The Rookie," an Orbital Drop Shock Trooper who crash lands in New Mombasa. You've been separated from the rest of your squad and you have to pick up the pieces of what's happened to them during the hours you've spent unconscious. ODST certainly presents a different mood and style from the primary Halo trilogy, but these subtle differences don't really detract from the playing experience. What changes have been made can barely be reflected upon in the gameplay. Instead, Bungie has players entering combat in a newer, moodier, darker atmosphere that really plays to the "alone in the dark" motif.
The Rookie explores the city at night, and boy is it dark at night. Parts of these sections were too dark for me to see, even with the visor attachment that lights up the landscape and outlines key points of interest: friendlies outlined in green, enemies in red, landscape in yellow, and story-specific objects in a noticeably brighter yellow. That certainly helps as you either pick off enemies from afar with your scoped SMG or pistol, but in interiors it was still too dark for me. I certainly felt like a rookie fumbling around in hallways and corridors looking for clues to where my squad mates had gone.
This doesn't mean that finding a clue wasn't fun, in fact I felt that this whole experience of find clues that led to flashback missions was really rewarding as a player. It's not like finding the clues are hard, they're very easily mapped out on the in game city map, but it was the feeling that I was given a cinematic and a mission filled with combat and explosions that made the fumbling around worthwhile.
Speaking of the in game map, it's provided by the Superintendent of New Mombasa, whose nicknamed Virgil. While this character is obviously inspired by some of gaming's latest robotic personalities (see GLaDOS), it doesn't speak very directly to the player. It provides the in game map (which kind of puts the exploring on easy mode) and directs the player from time to time with the city street maps. I found that throughout the campaign I was really glossing over any interaction with Virgil, he just didn't matter that much to me.
After each flashback Virgil also provides you with a resupply station so that you won't suffer the total lack of ammo there is in the game. I never really worried about having enough ammo in Halo 3 or any other Halo game, but for some reason I wanted to completely avoid the alien weapons but would constantly be out of SMG ammo. Worried that I'd never get the newly scoped weapon back, I'd hold on to it and use up all my pistol ammo. Of course none of it mattered in the end. ODST makes sure you have the weapons you're in need of, even if you might be running pretty low before finding the next ammo stash.
What low ammo meant to me as a player though is a choice between the longer route with no enemy encounters or the shorter route where I have to pick off some snipers and take down a brute or two.
One thing I'd like to note about Halo 3 ODST was the musical score. It was moody and contemplative during the rookie's over-world missions and driving and exciting during the explosive flashbacks. Some of the tunes just caught my ear and stood out above some of the other effects in the game.
Although I'm making note of one nice thing in the game, I have to say that the dialogue is terribly cheesy, and while the voice acting might suffice, it doesn't make up for the fact that I had to suffer through lines like "You're vote... just got overruled!" How very groan inducing!
If you're the biggest Halo fan in the world, then there really isn't any convincing you, you're going to buy the game, and so will plenty of other people. But if you're like me, you can probably get everything you're going to get out of it in a rental period.
PLAY READ WRITE / REVIEW SCORE: 4 OUT OF 5