I absolutely agree. Watching a game being played tells you a lot more about it than a couple thousands words about it's development cycle or who the people involved in making it are, or even describing an incident involved, or what it's like compared to other games you may or may not have played.This is definitely part of it. When I was doing them, all my reviews had a 1k work limit. A long review just isn't worth reading like a long news article is.
On the other hand, I'm totally down for watch a 30 minute review but that's because I'm getting more than opinion... I'm getting gameplay and that lets me decide on my own.
For example, I've never had much interest in GTAV - but seeing the AH crew do all the wacky hijinks they do in the game makes it look actually pretty damn fun.