Musically, Dragonforce remind me of Visual Kei, but without the image. I don't mind them. I think people dislike them because:
1. Lots of fast playing makes them feel inferior as guitarists
2. The singer has an old-school operatic power metal voice like Ronnie James Dio, which is perceived these days as a bit "girly" compared to most modern metal styles which have more of a growl or scream thing happening
3. Dragonforce have trouble executing their music live sometimes because of its complexity, and also have difficulty being interesting performers to watch onstage for the same reason. They are essentailly a studio creation.
4. Their lyrics seem pretty cliched and thoughtless. They're clearly only there so the singer has something to sing, they don't really communicate much. You could generate a HTML program to generate random Dragonforce style lyrics easily enough. Just get it to randomise words like "freedom" "power" "fight" "fire" "thunder" "pain" "forever" etc, add a few connecting words and there you go.
In a sense, this makes the band seem somewhat like a parody of themselves. But I think that's the point. They are in essence a cartoon of themselves. Which is where the "computer game" connection comes in. Dragonforce are a fantasy metal band with everything taken to the nth degree, and all the cliche poured on REALLY heavily on PURPOSE, just like Gears Of War is a macho action shooter with a "bigger is better" approach. Some people can't handle this "ironic hyper-reality" approach. Personally I like it - what I get from Dragonforce when I hear it is a sense of FUN and the idea that the guys are having a damn good time making this music. You can see it in the album sleeve photos where they're not trying to be tough guys, they're just posing stupidly with silly grins. It's a little bit "spinal tap" and I think that's a good thing. They have their tongues firmly lodged in their cheeks and are all the better for it.
And of course it all sounds the same, that's the style. Complaining about that is like listening to Bob Marley and saying "hey, it's all reggae, why doesn't he mix it up a little and throw in a metal number".