On one hand, I find it a little asinine when someone is reviewing a game and they say something like "It's not worth $30". Do you think it's worth $20? If $30 is as valuable to me as $20 is to you, should I get it? If I enjoy the game 50% more than you, should I get it? These subjective factors make the statement useless, and a time-wasting distraction from the rest of the review.
However, on the other hand, in extreme situations where the price is sky-high and the game totally blows, it makes plenty of sense. It's hard to draw a line, but $400 is a considerable chunk of change for most people. If you simply think the game isn't fun, there's probably not much harm in pointing out that the price is reason enough to avoid it.