I'm guessing your friend hasn't heard very much extreme music and just hears that it is extreme without recognising the seperate elements in the music. I can't comment Fiction as I haven't heard it, but an obvious thing is Character is alot faster. Damage done is also more melodically driven, introducing more soundscapes and less 'chugga chugga'. The vocals also sound different, DD being more classic melodeath and Character being really harsh and more aggressive, emotional and maybe a little less musical. I think the songs on damage done are also filled with more refrains making the structures a little more complicated and less typical than on character which sticks more solidly to verses and choruses, and even though there are some great instrumental sections in character, they're a little more predictable than on Damage Done, where sometimes the drums will relent and let the keyboards and guitars take the spotlight.
there's alot more, but they're some of the obvious ones I'd say. I'd also say even though character is a little more organic, Damage Done seems alot more soulful with genuinely more emotive arrangements and musicality on show. But that's probably just my opinion.