The GR review is more or less right on the money for this one. When it comes down to it this game can be summarised as "Halo, but you play as an ODST", which is definately not a bad thing. The comparison to Blue Shift is also quite accurate.
The first thing you notice when you play this game is your mortality. Being that one or two feet shorter and being able to take a few less plasma shots to the face makes a BIG difference; especially when you come around a corner and spot two hunters guarding a door. And notice they are about double your height. And they see you. And you realise the pistol isn't very effective. And since you decided to do your first run-through on Heroic they take about 3 clips of ammo to take down. Needless to say it was a very exciting freak-out that was much more enjoyable than any other encounter I have had with the creatures, which are too often just as easy to kill as grunts. I did notice the enemys getting a little repetitive though as theres no flood on earth in this part of the timeline and the elites are off god knows where rebelling you just have the brutes, grunts, jackels and hunters to deal with.
Which brings me to my first gripe, the exclusion of the battle rifle.
Ok so I haven't finished the game yet, but this weapon was my bread-and-butter in the final two games of the trilogy. What is more perplexing is that the carbine is included, I guess that they just wanted to put a little more focus on the silenced smg (which I admit is pretty cool, if ineffective). Oh which brings me to the first mistake I made, the smg and pistol may sound silenced, but the covenant act the same for every gun you fire, which I guess explains why they still haven't fitted a silencer to the sniper rifle yet.
As a side note you are able to wield the Gravity Hammer and Brute Shot and flip cars in this iteration, which normal humans could not do in any of the other Halo's. These aren't really things you could leave out of a game like this, but it does add continuity problems.
The music is of course excellent, if different. I think I liked the change to more mellow tunes but it is a little weird shooting things with jazz in the background. Don't expect big, epic choral pieces, after all this game isn't as much about the fate of the galaxy as it was in the trilogy.
Firefight is....well fun. There really isn't much more I can add to the GR review of this part, the exclusion of matchmaking is really strange though and quite unlike Bungie to leave something this obvious out. Here is to hoping for DLC. The added bonus of the multiplayer CD will help a lot of people that don't have the original H3 get into the multiplayer circuit though.
All-in-all a game I would recommend, though it's not without its shortcomings. It is an expansion pack remember?