To put it simply, the game is quite a bit of fun. It is a Team Fortress 2-esque game of 6v6. The attacking team either captures the point or pushes the payload to a point. The defending team stops them. Quite simple. I think it being that simple is what makes the game shine too. A central theme of the game and one that I urge any new player to experience is Hero Swapping. You are allowed to switch heroes during the match, with the only penalty being your Ultimate meter resets. I really like this idea, your team is not stuck with a disadvantage all game just because you chose a subpar hero for the situation. In League, if you chose a champion then get countered, you are stuck into that matchup all game. If you choose Winston in Overwatch and then they choose Reaper, then you can easily switch to a Reinhardt or Roadhog instead, which are not as easily countered by Reaper. The game is about creating an advantage from your disadvantage. Another interesting aspect are the classes. These classes are identical to those you would see in other games. Supports have utility and healing (usually). Tanks have health and utility. Defense are typically backline heroes but have a good amount of damage. Offense is a mix of front line damage and flankers (kind of wish they separate these categories though). Juggling these classes are key. In competitive there is a one hero limit (on here per team). In regular play there is no limit, but balancing these classes are still important. As a new player, and to keep in practice of Hero Swapping, if your team does not have a support and you are used to DPS, consider playing Lucio or Zenyatta; they are the more offensive supports. If you usually play something like Genji or Tracer but your team needs a tank, consider playing Winston.
TL;DR - Good game, consider trying it out (also, only pay $40 for it, don't buy the $60 option unless you benefit from it).