Choosing an apartment involves so many vital considerations that, in reality, it's no less complex than choosing a house. Size, pet policies, location, price, community amenities, and more play into this decision. There are a number of sites online that offer reviews of various properties but they are of differing quality and usefulness.
An apartment review needs to meet two basic criteria before it can be considered trustworthy. One, it should have been written by someone who actually rented the apartment, not the landlord or property management company. Two, the renter who wrote it should be someone who is well-written and rational. There are any number of "bad renters" out there and they can make a stay in any apartment complex sound as if it was the most horrible, unjust experience that anyone could have endured.
Really, because apartments are such a personal choice, a showing of the property itself is preferable to anyone's second hand opinion of the apartment. Apartment reviews can be useful, however, especially to those who are moving to a new city and don't yet know their way around town.
If you're deciding between whose review to rely upon for guidance, make sure all the reviews you're considering are comprehensive. A three hundred word diatribe about a bad paint job is really of little use to anyone. A well-written review that includes a description of the area in which the apartment is located, the quality of the neighbors, the responsiveness of the landlord to any issues that arise and other, important, information can be very useful. In particular, look for apartment reviews written by people with lifestyles similar to yours. If you're in your twenties and have an active social life, a review that mentions that the apartment complex is ultra-strict about noise complaints may give you some helpful information. If you're a retiree and you happen to want strict noise enforcement, it's useful to you, too!
Make a critical analysis of any information presented in an apartment review. If it sounds like the former tenant just couldn't get along with the landlord, keep that in mind before you prejudge the landlord too harshly. In fact, if the reviewer himself seems vastly different from you in needs and temperament and he didn't like the property, that might tell you something right there. An apartment review is valuable, but needs to be read with a critical eye.