What person A defines as something being trashed, person B defines as critisim. It is possible to enjoy something yet feel that it was lacking in parts.
VOY premise seemed to lean towards a more serialised show, yet we got a more episodic show. A fair few people don't think VOY ever really sold us it's premise hence why the show is referred to as TNG-lite.
Surely those who level critisim at episode for the most part tuned in weekly, so it held enough interest for them to tune in but whilst some are happy with what they got others felt it could have been more. Neither viewpoint is right or wrong, as we all have our likes and dislikes.
And yes "Shades of Gray" and "Spock's Brain" are bad episodes and they are both definantly towards the franchises bottom end in terms of quality.