Impact Exciter does two things with Nana Mizuki's voice.
First, it shows a bit of branching out stylistically -- while most of the music is hyperactive and ready for placement as theme music for cheap action series, it does spread beyond simple pop into space opera, remixed rock, and fast-tempo shouting.
Second, it shows that Mizuki's vocals might not be up to the task of branching out stylistically.
The compositions may initially vary in their instrumentation and tone, but with each bit of vocalizing, Mizuki seems to put them all into the same strained territory, desperately trying to keep up with the fast ones, to be loud enough for the rock-heavy ones, and to be soft enough for the light ones.
She stays in the middle no matter what, however, dooming the tracks to a sameness in their eventual result.
Mizuki has some emotion in her vocals, as shown in other recordings.
Here, though, she seems to be dispassionate in her delivery, waiting for the sessions to end.
The same goes for the listener.