Not all vacuum cleaners are created equal...in fact, they're actually not even close. When considering the features that make a good vacuum cleaner, it's a good idea to first understand that there are several very different levels of quality and performance when it comes to vacuums. Some economy-level vacuums are practically just toys-they do little more than sweeping the dirt and dust around a bit. These are the $99 variety you'll find at the box store. Probably a good idea to avoid this option altogether.
Other mid-range vacuums get the job done for the most part-but just aren't built to last or to be able to be properly maintained. In other words, they're disposable and very expensive in the long run. A true quality vacuum cleaner will be built to last, built to do the job right and get every last bit of dirt and dust possible contained, and most importantly, will be designed to last practically a lifetime.