@PotomacBobPeople working in these sorts of jobs need to consider their long-term career goals. Yeah, it's difficult to write positively about a genre you personally dislike, but giving a bad review to a decent book is a good way to burn bridges in an industry that is all about networking.
There are a few ways to deal with this sort of issue, but the two that I favour are detail-based reviews and research-based reviews (not industry terms, just a quick way to explain my point).
For this context, a detail-based review would be where you break down the book into a series of separate elements. Just because you dislike the story structure doesn't mean you can't get a feel for the narration style or pay attention to the descriptive elements, then write a review based on a series of separate parts.
Something like "the writing style is very action-based and moves quickly, descriptions are a bit weak and make it difficult to know what the protagonist is picking up on, characters are interesting if a bit archetypal, and the overall plot has a few fairly predictable twists before reaching a conclusion that doesn't rely on deus ex machina."
This reviewing style allows you to completely avoid the fact that you don't like the genre and focus on the individual elements of writing. The downside to this is that some readers will consider the review to be dry, disjointed, and unhelpful.
The second review style I mentioned, research based, relies on the reviewer doing research as to what elements fans of a given genre like. You don't have to be a fan of mystery novels to understand the difference between a story that gives the reader all the clues the detective uses to solve the crime and one that doesn't. You research half a dozen elements that fans of a genre consider important, then deconstruct the novel based on those elements.
The review then follows the lines of "Fans of mysteries where the reader has a reasonable chance to guess Whodunnit before the final reveal will be disappointed as the detective pulls the solution out of thin air, but at least the character's soliloquy in the final scene is well written. Serious genre fans should look elsewhere, but if you want a disposable summer read that echoes old episodes of Perry Mason, this might be just the thing."
In either case, whether or not you mention your own dislike of the genre is up to you, but you should take the size and community-mindedness of your readership into account. When writing for a small town paper or equivalent you usually want to cultivate a feeling that you're part of the community, especially if you're going to be on the job a few years. Telling people you hate their favourite genre makes it harder for them to take you seriously the next time you recommend a book. It's better to use a more neutral comment like "I don't usually read genre X, but ...".
Most importantly, when talking about reviews for a job, remember that your job may not necessarily be to give your own unvarnished opinion. There are lots of journalists writing in fields that they personally aren't interested in. The job is to produce content, not enjoy yourself. Do you really think that every female journalist spend four years in university just so that she can write a weekly column about gardening, pets, or dating?
As with any field, you start at the bottom with no control over your content and work up. Your ability to deal with the shit you don't want to do will determine whether you get the opportunity to do the stuff you do want to do.