Dragonforce is definitely a unique band. No one else manages to pull off such a combination of insane solos and mediocre lyrics. That being said, Dragonforce isn't a band you just listen to to enjoy the music itself. It is much better at purely passing time. On my recent trip to Pittsburgh, I was playing through Inhuman Rampage nearly the whole trip, and I have to say it did distract me from the tedious drive. And their songs are not the same. TTFATF is not the best song of theirs, it is just one of the more popular ones. The recycled lyrics attempt to be deep and epic, and when you realize that Sam/Herman are either flipping you off or holding a bottle of beer in all of their pictures just makes them even more ironic.
My favorite songs have to be Body Breakdown, Flames of Youth, and Cry for Eternity. They have the most "epic" feel to them and, more importantly, it is easily distinguished from the rest of their songs. Which I stress, are not the same. Even just a simple change in key or chord structure can make it sound much different.
Rating Dragonforce based off of their performance in GH3 is probably a disservice to them. I am sad to hear that their live performances are lackluster, but I can't say I would expect anything else. Half the reason I like to listen to Body Breakdown is because of the synthetic sounds in the solo sections.
I used to listen to Dragonforce almost exclusively for about 10 months, but after a while their songs lose some interest.