I think what I find interesting is that people complain about the story in Gears of War - it seems that such people must have their heads buried in the sand most of the time.
I'll give a quick synopsis, without any fluff: Humanity is being attacked by an irresistible force. All hope lies in the hands of a small team of exceptional bad-assess, who routinely succeed in the face of almost certain defeat. At the close of the first episode of play, the aforementioned bad-asses resolve the immediate problem, but unfortunately fail to ultimately resolve the problem. As the second act is revealed, humanity is found to be in even more dire straits than before, and the same team of bad-asses once again proves they are the only ones capable of solving the problem. Another of the great strengths of the enemy is revealed and quickly dispatched, and humanity concocts a wild scheme designed to end the war quickly. Unfortunately, by the end it seems as though they may have played into right into the diabolical machinations of some other ultimate evil force driving their enemy.
Basically, if one strips away the fluff, you'll find that it is essentially the exact same story arc seen in most every video game ever made. In fact, Star Wars and the Matrix are two notable movie trilogies that follow this exact same pattern. If this specific story arc pattern can be heralded in other games and media, what exactly is the problem? I'd say we need to look at the culprits:
Dialogue - some people will say that the game has laughably bad dialogue, and they may have something there. That said, we must consider that every single major character in the game has fought a brutal losing war for most of their lives - such things are almost certain to erode one's capacity for motivating speech. When one is forced through necessity to meet problems with nothing but brute force and firepower while watching their friends and family be claimed by an unstoppable force, resorting to gallows humor is really the only place one can go for a laugh.
Characterization - I will admit that there is poor characterization, but that is not really the fault of either story or universe, but rather by the games basic design. During the game, the player will confront problems through the use of firepower and heroics, and any other character traits are revealed in cut scenes. Since 99% of our experience with the characters is found in firefights with the locust, any traits revealed in a cut scene that do not meet the limited knowledge set we gain through gameplay are discared as "tacked on". This is a problem with any media that focuses on action to move the plot forward. Were the game to focus more on better, consistent characterization, there would inevitably be wild swings in the play dynamic and pacing, or it would be force to travel down the dark road of Metal Gear Solid where one spends as much time watching movies as they do playing the actual game.
Universe Specific Plot Points - Again, I see nothing really wrong with this factor. Locust may be aliens, or perhaps mutated humans. Either way, they represent a sufficiently foreign force that helps clearly define who is a "good guy" and who is a "bad guy". Star Wars accomplished this by ensuring the bad guys wore shiny armor, or dressed mostly in black, while the good guys favored a less conservative garb with a wider variety of color. The focus of immulsion as an energy source and perhaps original cause of the conflict is another point - at least there is a reasonable motivation for people do so silly things; desperation is the mother of most stupidity. In Star Wars, the key motivation appears to be a grab for power, and I tend to think of power as a means to an end, not the end in and of itself. (Actually, I've never understood exactly WHY the Palpatine wanted to rule the galaxy, given that he really didn't seem to have any grand schemes on what he would do with said power). It seems that the universe specific plot points are actually quite suitable for the world the game takes place in and provides a reasonable basis for the game's actions. Again, the story could be improved here if there were more time to explore in greater detail each piece and character, but doing so would inevitably harm the action oriented gameplay.
Considering just what KIND of game Gears of War is, it actually has an excellent story. Yes it has glaring weaknesses, but it would seem that the only way to resolve those is to change how the game is played OR explore the back story and motivations in greater detail in other media (graphic novels seem like the most logical approach). The story in GoW as such complements the gameplay, and never seeks to become the focus. In essense, it provides a rich framework in which to paint a beautiful canvas of brutal violence and deeds of inconceivable heroism, and I think that's enough.
And, as an aside, can anyone think of any mainstream action game that has a truly better story? I can think of a host of RPG's that do, of course but the story in an RPG is a key part of the experience. Half-Life's story is no better, it just does a better job of characterization. Call of Duty and other war games don't have a story so much as they exist within the framework of a narrative, and I'd only be willing to grant that CoD 4 may have a compelling, original story, but characterization and dialogue suffer for the same reasons they suffer in GoW. Assassin's creed seems to be following the very same story arc, based on one episode of play.
In short, is there some action game with a magical story that I am unaware of, or do people rip on GoW's story because it's popular and they can handily point to in order to seem as though they are the sort of person who truly values the story in a game primarily about killing people?