I haven't read any of her Voyager work, so I can't speak to how Fire Ship treats the characters.
"Fire Ship" is a Janeway solo story or, rather, Janeway as an underling on an alien ship, stranded far from her Voyager crew over a period of months. It's from the period between the change from the infamous "bun of steel" hairdo to the more casual look that Janeway had in later seasons and, as such, is a nice character arc. The other "Voyager" crewmembers are barely in it.
I found it a real page turner, with some believable, different, alien tech, and a story on a par with the "New Frontier" installment of "The Captain's Table". Very strong stories!