I don't generally read what other people have said about a game before I leave a comment with my review, though I sometimes skim them afterward and feel a bit self-conscious if someone recently said basically the same thing I did. I don't think that's actually a bad thing to give similar feedback as other people and the most important thing is to relay my personal experience as a player of the game, how it made me feel, what I liked about it, what I thought could work better and so on.
As a developer you only 'need' to hear about a bug once to know it's something which needs to be fixed, but for honest feedback it's helpful to know how often that bug is being encountered and how much it's affecting the experience of players when it does happen. Likewise, if a lot of people praise the same aspect of your game it doesn't mean they're simply grabbing something to be positive about; it probably means that's what makes your game stand out in the minds of many different people, which is very good information to have.
If you want to know about a specific thing in your game, you usually need to ask people about that directly. Fortunately that's where the ratings help, on Monday we'll see what people thought of our games in several different categories, averaged out. Still, don't take those numbers as absolutes and don't take any single comment as being definitive. Ten comments about ten different things in your game shouldn't have the same weight as five people who all agree about a single aspect of your game and felt like commenting on it.
Or that's what I think at this time. :)