Not surprised, the PC/Console gaming market is ATM unforunately dominated by a few large games and their equally large developers. This leads to smaller developers playing copy-pasta and making even original games dull and boring because they copied the combat/build/theme of X popular game because they develoeprrs went "ooooo, it's popular! lets do that and make lots of money!"
It's also dominated by an excessive number of sequals. how many Halo games are we up to? We've now on what, the 3rd expansion to WoW? We've got Dragon Age getting a sequal which has more recons than a superman comic, and we're up to Mass Effect 3 where your immortal-cyborg character is about to take on an army of god-robots.
So it's not surprising that amid all the unoriginality and the repition, that players are going: "Hey, I can do better than this." or "Ooo, good idea, but now I want to add this, or remove that and make it better."
Respectfully, I think you're missing a few things here.
First, Halo: Reach (the newest incarnation) is one of the best-selling games of all time, and it outsold Halo: 3 on opening day. In other words, it was a huge success. And this carries on with all of those games you've mentioned - sequels are made because the gaming public WANTS them.
Second, Sequels in video games are done for a few reasons - the primary being that it is easier to make a game based on past work (ie, using the old engine and tweaking the gameplay, rather than starting from scratch). If you're running a software company, would you rather spend 2 million to release Awesome Game 2: The Sequel or would you want to spend, say, 12 million to release a game completely unrelated, and hope that it catches on? Fact is, game one will probably sell more units than game 2, and for a cheaper production cost, to boot.
Third, there is always a downturn in Q3 sales for video games, because all the big games get released in Q4 for Christmas. Developers (and gamers) know this, so you tend to see a reduction in the quality of Q3 games, with gamers also reducing their spending budget to save up for Christmas.
Also, smaller developers tend to release original games, with the middle-stream developers trying to play catch-up with the big guys. The smaller guys often run 3- or 4- man outfits, and release smaller-scale, addictive games. Simply go on XBox live arcade to see an example of this. They specialize in making cheap games that are still fun - while they may not see the millions in sales, their overhead is small enough that it works.
But when you run a big software company, you don't want to spend millions developing a game based on a new gameplay experience - it's much smarter to try and copy what the big guys are doing, and instead attach some tweaks learned from their mess-ups. And remember, this is how games like Halo, Dragon Age, and Mass Effect started - taking an existence genre of game and reworking it.