The problem with reviewing F2P games is that they are so prone to change over time. Someone might stumble upon a review a few months after release and the review won't actually apply much to the game anymore. It's the same reason they don't review MMO's and things like Sims expansion packs. The only reason F2P games stop changing is because people don't play them anymore, and then there wouldn't be a need for a review anyway. I think the quick look or bombcast opinions are good enough for you to know whether to make a gamble on it. If they've already said they think something is quite good, I don't mind spending 2 hours on it to see if I agree or not, as it hasn't cost me anything. I can always not play the game after that!
DOTA 2 is a unique outlier in this. Even other MOBA's don't take so much time and even you Brad might tell you how awesome it is at the end of 200 hours played, it's still pretty awesome after 5-10 hours. Also you could try a simpler MOBA first.
EDIT: And also, do you think you might know what Brad might say in a review for DOTA 2? I reckon he might says "it's damned awesome and you should give it a try. It's free after all." There we go, no need for a review anymore!