I guess it depends. If you played 5 hours and it absolutely didn't capture you then you could write about your experience and why you didn't feel like continuing. It certainly wouldn't be an academic study on the game, but it could be important information to potential buyers. I agree that the main review houses need to play the game for days and days to get a feel for it so they can justify their score. But they have a different level of commitment to a review than the typical user review.
I haven't played the launch game, but, unfortunately, I found the beta rather bland. I think the problem I had was going into the game thinking it was extremely open like Borderlands where you can run around enormous maps, stumble into quests, and everything was directly connected. Destiny is set up like a hub world where you click on places to go to comparably smaller maps that do not interlink with others. It was also disappointing to have maps recycled so often as well.
My ignorance for the game drove that bad taste though. If it hadn't been compared to Borderlands so often then it would have felt extremely open compared to Halo. I'll probably end up getting it, but I've got other games to beat right now.