Apple calls it the "the biggest leap forward since the original iPhone," Walter S. Mossberg from The Wall Street Journal says it's "the best device in its class" and consumers are giving the device a nod (many without even setting hands on it), racking up more than 600,000 preorders in one day and depleting retail stores of their entire iPhone 4 inventory.

But what makes this new device stand out from the saturated market of high-powered, feature-rich smartphones? What are the issues you should be aware of before purchasing the device? Relaxnews goes hands on with the iPhone 4 to find out.

The first thing that makes the iPhone 4 stand out from the pack is its striking industrial design: the phone comes encased in a chemically-strengthened glass and is finished with a stainless steel band that wraps around the outside. The new design replaces the iPhone 3Gs's plastic-y feel and makes the device feel solid and well-constructed.

The stainless steel band doubles as an antenna for the device, which is now known to cause problems in the reception when the device is held in a certain way. This can be rectified by moving your hand or purchasing a cover for the device says Apple.

Aside from the design, the most noticeable upgrade is the new Retina display (the boost in speed and extended battery life come in a close second and third). While handsets like the Droid X and HTC Evo 4G might wow you with the size of the screen, multiple tests show that the iPhone's 3.5 inch, 960x640 pixel display is leaps and bounds ahead of the competition.

As Cult of Mac writes in their iPhone 4 vs Evo 4G screen test article, the iPhone 4's display "is the new standard for smartphone displays. Sadly, though, this means your brand new iPad is going to look this muddy once you get an iPhone 4 in your hands too."

Some consumers have reported seeing a "yellow discoloration, either as a thin line of yellow or as a circular tint" on their display. The problem is thought to be caused by a bonding agent used in the manufacturing process and has, in many cases disappeared after a day.

The new 5 megapixel (MP) camera and addition of an LED flash make it possible for you leave your point-and-shoot digital camera at home. Images taken with the phone appear clear and crisp on the screen and when printed on photo paper. iPhone 4's camera, however, doesn't compare to the 12 MP camera found on Nokia's flagship smartphone, the N8, or even the majority of 8MP cameras seen on many new smartphones on the market today.

iPhone 4 may, however, have compact camcorder makers worried. For example, both the iPhone 4 and the Flip Ultra HD are very compact and provide users with 720p (high definition) video at 30 frames per second, but the iPhone 4 also provides users with touch to focus, more storage, onboard editing with iMovie (an app that will set you back $4.99) and a large range of additional video-centric apps.

Another feature Apple is very proud of is FaceTime. While the concept of video chat is not new, Apple makes it so simple to use that consumers will opt to use FaceTime over competing video chat applications such as Fring.

The ability to easily switch between cameras on the iPhone 4, seamless contact integration, and lack of user set up/configuration required make the whole experience much more engaging.

The Retina display, processor upgrade, HD video recording, video chat, iOS 4 and the phone's new sleek industrial design means that (despite known flaws) the iPhone 4 is the smartphone all the others will have to beat. Here's to the next wave of "iPhone 4 killers."

Want to know how the device compares to the Flip, N8, Droid X and Nexus One? Check out the side-by-side comparisons below.

Flip Ultra HD Video camera vs iPhone 4:

Nokia N8's 12 MP camera vs iPhone 4's 5 MP camera:

iPhone 4 vs Droid X:

Round-up of the competitors:

iPhone 4 vs. EVO 4G vs. Incredible vs. Nexus One:

Consumer reviews:

Fring vs FaceTime:

Engadget's review:

Walter S. Mossberg's review:

Known issues, "blemishes" and problems to be aware of:

5 Big Blemishes for the Apple iPhone 4:

Critical iPhone 4 Issues and Complaints Are Mounting:

iPhone 4 Problems Start Piling Up: