Overwatch is a hero based first person shooter (similar to Team Fortress 2) where teams of players with different roles (such as offense, defense, tanks or support) combat a similar team in a different game modes (such as escort, assault, hybrid or control).
Pro Unique FPS gameplay
Overwatch combines traditional team-based FPS elements and MOBA-esqe characters with unique abilities and weapons. You'll still be shooting and bashing your way to victory, but instead of picking different weapons, you'll be often switching between one of the many characters. Each character has its own strengths, weaknesses, and unique playstyle.
For example, there's Tracer that dual wields handguns, is pretty quick on her feet, and can rewind time when in a tough spot, which makes her well suited to hit-and-run tactics. However, she has poor aim and low health, so you have to be a lot more careful when playing as her.
Another example would be the very durable Reinhardt who has high health and armor. He's able to protect his allies and himself with a projected energy shield while moving at a slower rate. Unfortunately, his only real means of attacking is a giant hammer, so fast characters or characters with a long range can easily outmaneuver him.
As a result, Overwatch not only rewards accurate shooting, but also quick decision making and clever use of your abilities, creating gameplay that feels different from most competitive FPS games.
Pro Variety of maps to keep gameplay interesting
Overwatch currently has 16 maps, which includes a Moon colony, an encampment in Antarctica, and various futuristic cityscapes. The distinct themes, color palettes, and layouts make each of the maps feel and play differently, keeping the gameplay fresh for a long time.
Pro Tons of unlockables to keep you playing
Each playable character in the game can have more than 90 different unlocks such character skins, color schemes, emotes, and victory poses. While these don't affect gameplay, they allow you to create a personalized character you can feel more attached to. This gives additional goals for both regular players and completionists, keeping the game interesting for a long time.
Pro Simple to learn and play
While Overwatch has MOBA elements, it's very simple at its core, you just shoot the enemy and take objectives. It may take a couple matches to get the basic down, but from then on it's gonna be a blast. This makes it a lot more accessible than most MOBA-esque titles that take a really long time to learn and master.
Con No content creation tools
You can't create custom maps or game modes, which considerably limits how much the community can contribute for keeping the game fresh and exciting. This is a step back when you look at the Warcraft 3 map editor, which helped the game stay popular a decade after its release even without regular updates from Blizzard.