I struggled with this game initially, because I couldn't accept that I had to play it on the lowest difficulty setting. After getting over that mental block, I had a lot of fun with it.
Gears of War is a third person shooter that ends up playing a lot like a first person shooter, but with the benefits of getting to see your character run around the world in all his beefy glory. With so many shooters on the market, so many attempts at new gameplay ideas, it's hard to come up with much new that's worth having. Gears of War manages to streamline and make good on a mechanic that other games have tried to varying degrees, and add a few wrinkles of its own.
At the core of GoW is the cover mechanic. Your character will lean against doorframes, crouch behind low walls, and lean in and out of these cover elements in a relatively seamless and intuitive fashion. There are certainly moments where this can go wrong, and you find yourself sticking to something you didn't intend to, or failing to take cover when you'd want to, but for the most part it works well. It creates a sense of tactical movement, and indeed forces the player to use cover, to move tactically, to suppress the enemy, and not to just run around blasting at things. When this mechanic works, it really works, and all the fun, memorable sections of this game revolve around it.
Another nice touch is the rapid reload mechanic. A little timing bar appears under your weapon on your HUD as you reload, and if you hit your reload button at the right time, you can reload faster, or even gain a damage bonus. Hit it at the wrong time, and your character will fumble the reload, taking even longer, and cursing his failure. It's not hard to get used to, but it adds another element to gunfights, creates another point of rythym, so that when a player is on top of things and in control, they feel the reloads, and when they're out of sorts and hurried, they lose it.
Graphics are also very good, both technically and artistically. The big beefy character models are great, and the cartoony facial animations are effective and interesting. The world is very detailed and immersive. My system felt a bit overtaxed at times, but I made no effort to tune the settings to get better performance. It was a bit choppy, but not unplayable. The game really looks great, and feels solid and gritty. I was particularly impressed by the bouncing, chaotic feel produced as your character races forward with his head down, avoiding fire. It's a cleverly realistic simulation of the tunnel vision one experiences in such a situation.
The weapons are good, although perhaps a bit feeble, as it often requires extended assault rifle bursts to down even basic enemies, although blind firing around cover, or letting loose from the hip can be bloody and fun. The Torque Bow is also particularly fun to use.
All the good news aside, GoW does have a few issues which keep it from being perfect.
One is that it leans too heavily on the “babysit the AI” mechanic that squad based games suffer from. Your squadmates are fairly useless, and fairly brainless, often running into situations that get them killed quickly. This is less of an issue on lower difficulty settings, where they're also less vital to your success, but it's still an annoyance. They never actually die, but they will lay there and moan at you until you come over to help them. In a game that's generally top notch, they're awfully brainless.
Another issue is the occasional gimmick fights that are frustrating to deal with, and generally add nothing to the gameplay. The fights with the blind Berserker enemies are a particularly good example. Periodically the run and gun gameplay will be interrupted by a scene in which a Berseker shows up, a monster you can't kill with your normal weapons, and you have to somehow fool it into a special tricky way of getting killed. The trick is obvious immediately, but getting it pulled off is incredibly tiresome, especially with your squadmate randomly letting the Berseker kill him (this is one way your squadmate can actually die).
The biggest issue is the difficulty settings. There are only three levels, Casual, Hardcore and Insane. Initially Hardcore is very doable, but rapidly becomes pointlessly difficult. Casual is generally too easy, but at times challenging, particularly later in the game. A big part of this game is to play in co-op mode with another player. This explains why the Hardcore and Insane levels are there. With another human, instead of the extremely lackluster AI, Hardcore would be very doable, and (I presume) Insane as well. But, considering that the difficulty settings seem to mainly effect damage taken and damage dealt, there's really no reason for not having a finer level of tuning, certainly something between Casual and Hardcore.
All in all GoW is a great game, one that sets new trends and creates new ideas in the genre. Its issues are comparatively minor, but so unnecessary and easily avoided that they really stuck out for me.