I finished the single player campaign in one sitting of about 6 hours yesterday, though admittedly it was on 'Normal' difficulty.
I was beautifully cinematic at points, particularly the Ark which had some gorgeous matte painting style backgrounds. Some of the cutscenes used a depth of field blur effect that was very convincing, probably the best I've seen in a game so far. Also the HDR lighting was implemented very nicely (best seen when a Scarab explodes), I take it this is because they used an additional frame buffer for lighting effects and combined it with the primary in post processing.
-Spoilers follow-
There were a few confusing or unsatisfactory points in the story though.
The lead up to meeting Cortana is handled well and was emotionally effective. She was such a light hearted character in the previous games that hearing her obviously distressed really did make me feel that I wanted to race ahead to save her. The fact that it's heavily implied that Gravemind has (in a sense) violated her and already done extensive damage adds a sense of dread at what what state you may find her in. She implies she can't be trusted and is not even the same person any more ("I'm shadow of my mother") and when you do find her she says "Parts of me feel so wrong".
But don't worry, then she's fine! Seriously, after you plug her right back into your helmet *great idea Chief) she delivers about two lines of dialogue where she sounds distressed and then the old Cortana is back and is
just chipper. I guess she must have run the Chief's built in anti-virus scanner on herself and cleared the whole Gravemind thing up. They obviously wrote themselves into a corner with that one, as you can't really stop the action in a game like Halo to have one of your characters explain to the Chief how she was virtually raped and enslaved by an insidious alien intellect - the core audience will start eating each other if the Chief doesn't kill something every fifteen seconds.
One thing I thought was funny is during the early parts of game Commander Keyes stands in for Cortana's while she is missing. It's almost as if Bungie was so terrified of changing the
winning formula (remember guys, everybody hated the Arbiter bits in Halo 2!) they decided they just had to have an attractive-young-female on the radio to you barking orders at all times. Hilariously as soon as Cortana shows up in her old role Commander Keyes is quickly done away with by a Brute. Oh and why didn't the flood infect and re-animate her body just as it did for every other dead body all around her? It even starts infecting the Prophet while he's still alive.
And another thing! What the hell is with the marketing for this game?
The awesome huge
The-Master-Chief-is-Jesus-Christ diorama depicts a scene which apparently never happened. That's right, that striking image of the Master Chief's limp body being held aloft by a triumphant Brute Chieftain in a scene evocative of dramatic renaissance paintings of battle? Yeah, not in this game sorry, not even anything close to that happens.
The video shorts where the old soldiers hauntingly recount their feelings about battle and the horror of war don't make sense in context either; all the Marines I met in the game were having great fun. There was a total of one Marine who was upset, and that was because he saw the Flood transform his Officers into monsters in front of him. Otherwise everybody else just yells "Yow that smarts!" when they take a plasma round to the face and then continue to drop amusing one liners. Even the severely injured Marines just lie there in dutiful silence, trying their best not to give the impression that war is anything but a bit of a light-hearted romp.
All that said it's still a very enjoyable game, the combat (as always the main draw in Halo) is just superb. There's many ways to approach each combat situation and even if the differences do eventually boil down to how many bullets you shoot at the enemy and how fast, it still leads to some enjoyable tactical nuance that had me frequently trying trickier sections with different weapons rather than continually assaulting with the same ones again and again.