Finished the game this morning..... twice, actually. 
I started up a Normal mode game, and played it concurrently with Hardcore. I was curious to see exactly what the difficulty changes were between the two modes, plus Normal gave me the opportunity to sweep for all 42 collectibles and 15 COG tags in order to earn the "Hoarder" and "Remember the Fallen" Achievements respectively.
While I still hold Gears 2's single player campaign in higher regard, thanks to its sharper pacing, and bigger, more memorable set pieces (nothing beats the likes of the ride to Landown, the Rift Worm -- and yes, the New Hope lab facility), Gears 3's campaign is still wholly satisfying. Controls are as refined as ever, there are plenty of new and varied locations (all graphically gorgeous), the action is explosive with nary a lick of screen tearing or framerate drops, and they've mercifully done away with manual-driven vehicle sections. Story-wise, we get closure for the most part, and the ending feels like an appropriate cap off for the trilogy. (FYI, you do tend to get more out of the story and characters if you've become invested in the Karen Traviss novels. Characters like Sam and Jace have more of a justified reason for just being there in the game.)
Again, about the only downside is your teammates' overly capable AI, which I suppose could be argued that it's dint by design. It's clear that Gears 3 was built specifically for multiplayer co-op in mind, and I'm still trying to decide if reining back the AI as a solo experience would have helped or harmed it. Yes, I've bitched and ranted about the game being too easy during its first half, but right around when the challenge started to ramp up by Act 4, I've come to rely more and more on my squad's reliability. I was downed more times than I could count, and honestly, would I have really wanted to go through the aggravation of constantly seeing that Game Over screen and reloading checkpoints instead of being revived on the spot and having another go right then and there?
Playing on Normal mode was certainly an easier affair than on Hardcore, but what I noticed is that you had more opportunities to get yourself into the fight before your teammates, and so you'd have a bigger enemy count for yourself. Taking less damage means getting downed less often, so you're likely to get steadier, prolonged beads on your foes. In some ways, Normal was a more enjoyable affair as a result.
In any case, I'm looking forward to actually participating in a co-op game, just as soon as I renew my lapsed Live Gold subscription -- as well as try out the rest of the multiplayer modes. See how Insane fares, too.
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Acts 4 and 5 spoilers:
-Act 4 played host to some big, challenging firefights. The one heading to Griffin's refinery tower, just before seeing the cable car in front, was a notable highlight. This was the first big skirmish since the courtyard battle in Gears 2 that I had to hash out a solid strategy for. Didn't help that my supplies were sparse to begin with, a notable lack of Lancer ammo in particular.
-Much of Act 4 felt like one big fetch quest, but we do get two interesting new enemies to fight. Check that: two massively PAIN IN THE ASS enemies to fight. The Serapede on Hardcore was particularly irritating, since one hit from its electrical shock was enough to down you. And as soon as one of your teammates tries to revive you, it would nail the both of you in one swoop. Then there's the Armored Kantus, which can be tough if you don't know exactly what you're doing. Boomshot or Torque Bow are your best pals here, but without them, timing your frags to stun them can be a tough endeavor. (Grenade tossing is still shit in this game. I really got spoiled by Uncharted 2's pinpoint accuracy.) And goddamn, what a pain it was fighting both Serapedes AND Armored Kantus in the same area. Soon as I got a Kantus stunned, my precious window of opportunity to shoot him in the mouth was usually robbed thanks to the Serapede getting in my face and electrifying my ass.
-The Gorgon SMG pistol is much more useful now, thanks to the new automatic firing mode. I learned to use it lots after the several Armored Kantus encounters. (Speaking of weapons, I wasn't a fan of the Retro Lancer. Never had much of an opportunity to use the Sawed-Off Shotty, and while the Cleaver and OneShot are specialty weapons, they were fun to use when the occasion arose.)
-These games show their seams whenever it comes to vehicle sections. Luckily, Gears 3 only has the truck chase to Mercy, and the submarine sequence -- and they're both on-rails, at least. Those lousy underwater mines. And I'm curious: is this the same Leviathan as the one we fought back in Gears 2 and the opening Act of Gears 3? It'd be great if we could finally put this puppy down for good someday.
-Outside of Uncharted 2, Act 5 boasts some of the most beautifully rendered graphics and effects I've ever seen on a console title this generation. The Maelstrom's darkened rain clouds and lightening storm, the bright, idyllic vistas on the Azura Coast, the luxurious decor of the hotel, and the fire effect of Queen Myrrah's Tempest attack is simply unreal. Time to step up your game, Uncharted 3!
-There were two collectibles that drove me up the wall with frustration trying to acquire. Both on Act 5, one in chapter 1, the other on chapter 2. You need to keep the Silverback mech you get for the entire duration of 5-1, and a fair chunk of 5-2. Not easy, especially on Hardcore.
-Jack is back! His new stun attack really did come in handy during a few hairy moments.
-Loved how the "Gears Keep Turning" main theme was utilized during the last wave of battles. The sense of finality was hitting home at this point.
-It's funny how your very first attempt at a final boss battle almost seems like it'd be the most successful. I died at what would have been the final Hammer of Dawn strike against Myrrah, only to have to attempt it about ten more times, each with varying degrees of success -- but every one of them, save for the last, never coming close to how far I'd gotten on that first try. Brilliant use of the cover and pop-out/shoot mechanic for this battle, but nothing was more infuriating than having a stray Locust sneak up and Lancer-shred you from behind.
-See, I KNEW Dom's knife would play a role eventually. The cutscene back in Mercy when he first gave it to Marcus did feel more relevant than it was letting on, and I'm glad my inkling turned out to be correct.
-Some plot holes still remain unresolved, but they're not significant enough to dampen the ending for me. (Though I'm still disappointed they didn't bother to tie up the New Hope/Sires plot in any way. I was almost sure that "Ruth" and Myrrah were going to be one and the same.) I was secretly hoping Marcus' do-rag would come off by series' end, and lo and behold! (I was hoping for some war-torn premature gray hairs. The books very clearly mark that description.)
-And I completely forgot about Carmine until his heroic reappearance during the final battle, totally falling for his split second fake out death during the ending sequence. CARMINE SAVED. Good show, Epic. Good show.
