I thought I'd just list a few things I liked and disliked about Gears of War 3. Warning: SPOILERS!
LIKED: The series finally spent more time outdoors than indoors or underground, and we got to see some color. I liked that. The near-monochromatic color scheme worked well in introducing the game world back in the first game, but as things moved faster and became more crowded, it became monotonous.
DISLIKED: GoW3 is only marginally less set-piece happy than GoW2 was, with plenty of sequences that turn the experience from a third-person shooter into a rail shooter.
LIKED: I liked how we got to see how the actions of two separate squads came together to result in the defeat of the game's first boss enemy, the Leviathan.
DISLIKED: I disliked how jarring the transition was, going from Marcus and Dom defending the ship, to Baird and Cole looking for groceries. Ultimately, though, the gameplay for the second team was more enjoyable.
LIKED: I liked that we finally caught up with Dr. Fenix, finding out that there were at least attempts to make peaceful arrangements with the Locust as they came to the surface, fleeing from the Lambent and coming into conflict with humaity.
DISLIKED: I disliked that it's never made clear whether the nature of Imulsion itself made the Locust-Humanity conflict unavoidable, or if it was humanity using it as a fuel that exacerbated the problem.
LIKED: GoW3 brought Sera's women into the team as active characters, doing what the player is doing-- fighting for their lives instead of just providing support.
DISLIKED: The game still tried to achieve emotional impact it really isn't up to; much like Dom's quest to find his missing wife, Maria, that resulted in a much too quick decision to perform an ad hoc mercy killing, Fenix in this game suffers the loss of Dom and then his father. As in the last game, what emotional impact the game gets from these scenes is nearly erased by glib in-game dialogue between squadmates about "getting over it" and other such nonsense.
LIKED: GoW3's Lambent enemies evolved much as Halo's Flood evolved, becoming unique units rather than just "infected" versions of Locust enemies.
DISLIKED: Unlike the Flood, the Lambent never get their own motivations; the game calls them parasites, although parasites that kill their hosts are generally unsuccessful, and parasites that make their hosts homicidal maniacs don't do much better.
Lest anyone think I'm being too kind, here's one last big DISLIKED:
I really thought, going back to the first game, that what GoW was building up to was a "we have seen the enemy, and he is us" moment. It made sense to me; this planet is called Sera but our protagonists are human and refer to themselves as such. That seemed to indicate to me that humanity colonized Sera, and that the Locust are a native species. As such, what humanity perceived as surprise aggression from an unexpected direction could have been interpreted as the Locust defending seasonal territory. Their very name seemed to suggest a seasonal cycle, perhaps one so long that an entire human civilization thrived on the surface during a period when the Locust were dormant underground.
Sadly, this is never recognized, and all the emotional payoff in the final chapter is about humanity's revenge on the Locust; there's no rapproachment at all, and no acknowledgement of any fault on humanity's part, despite Dr. Fenix's involvement in making weapons of mass destruction that killed millions on both sides, as well as his concealment of the Locust from humanity before E-day.
Plenty of other threads are just dropped and ignored. Queen Myrrah's announcements about the Lambent in GoW2 sounded matter-of-fact, almost as if conflict between Locust and Lambent was a regular occurrence. The mechanically-triggered raising/lowering chest high walls throughout Locust cities seemed suggestive of regular, perhaps even ritualized combat underground that could not have been taking place between Locust and humans, but might have been taking place between Locust and Lambent. A cyclical struggle for dominance seemed indicated, or perhaps a contest over the right to live on the surface. The reveal of the Lambent as a worldwide parasitic infection makes all of that irrelevant, and still leaves unclear humanity's role in the ongoing conflicts both above and belowground on Sera.