There are a number of different styles of firearms.  Some are practical, some are fancy, and some have evolved from a specific or special use.  The titles I give these "categories" are entirely my own, because I haven't heard any formally accepted ones.  While I've illustrated the groupings with pictures of rifles, they apply equally to pistols.  Let's take a look at what's out there.

• Antiques:  Guns have been around for a long time - hundreds of years.  The US government doesn't even consider guns made before 1889 to be "firearms", that laws apply to.
  
• Fancy / Ornamental:  There was a time when a person's gun said something about them, maybe they way a stylish watch may make a statement today.  A prominent person might carry a gun with a distinctive ornamentation.  There are also many "collector's" firearms that may be similarly adorned, to commemorate certain organizations or historical events.  While some of these guns may be completely functional, others may be realistically unintended for actual use - owners may be reluctant to use them either way, for fear of damaging them.
  
• Modern Utility:  Many guns of the last century, including military arms, have been designed for hard-working daily use, and were reasonably priced.  These guns will use characteristically modern cartridges, and may have sophisticated and precise mechanisms.  Without any unnecessary frills, but possessing all the features to serve their purpose well, these guns will continue to give their owners shooting enjoyment for decades or centuries.
  
• Modern Tactical / Combat:  In the past handful of decades, the advances in modern combat techniques have led to a range of evolutions in firearm design and features.  Many of these guns have a characteristically "military" look, desired by many shooters.  Regardless of the aesthetics, they include many great features to increase the shooter's accuracy, allow the mounting of optics and accessories, and adapt to a variety of uses.
  
• Hunting:  Guns made for hunting tend to have a unique and identifiable style, due to their special use and the distinct hunting culture of their users.  While sometimes this manifests very obviously in the form of illustrations of popular wild game, or the application of ultra-realistic camouflage patterns, it's often more subtle too.
• Target / Competition:  Firearms designed for highly accurate target shooting, or competition, typically include many overt features designed to aid the shooter.  The rules of competitive shooting, such as the stance you must use or gear you can have, breed an array of unusual changes.  Some of these include thick / heavy barrels, elaborate peep sights, weights added for balance and stability, muzzle devices to compensate for recoil and muzzle climb, and flashy team colors.