I haven't decided which is worse: their music, or the fact that threads like this pop up entirely too often.
I believe all the specifics about why people don't like their music have been made clear by previous posters (highly technical playing with zero musical substance, etc). Far more annoying than being ear-raped is the fact that some fans won't just let the issue die. The debate has been going for several years, with no clear victor to date.
The worst thing (for me) about Dragonforce is that their fans are completely convinced of their awesomeness, and often (not always) take it to evangelistic levels of annoyingness. This doesn't mean that Dragonforce fans are wrong to believe such things, but rather they are wrong to "take it to the streets." Easily the most un-metal part of the Dragonforce craze is the overzealous fanboys.
To the Dragonforce fans: please, just let it go already. Some of us don't like the band, some of us don't like the fans. It's incredibly easy to fix one of these problems. It starts with not fighting over this anymore. When all the pointless debate is over, pick up some Dream Theater and see if you like it as much.
To my fellow haters: We stand little chance of converting Dragonforce fans by such meaningless pandering. Leave them alone, and maybe they'll just drop the issue once and for all. Perhaps recommend transitional bands instead of building a wall to keep them out of the "good metal".