The complex gameplay mechanics combined with detailed audio, graphics, and lore makes this game a true masterpiece.
Gameplay:
The game does not stop at just picking a character (known as hero in the game), you also have to build the hero buying special items and learning various unique abilities/spells as you level up. Although the objective of the game is pretty straightforward: destroy the enemy base; it is quite hard to actually get the hang of the character and understand the innumerable complex mechanics of the game. Moreover, since you are set on playing with four other humans on your team, teamplay and communication becomes very important as you climb through the matchmaking ladder (meaning: as you get better at the game). Valve did a really good job at developing a very balanced Match making system, so when you first start the game, you have a good possibility to end up with people who are new to the game like you. It takes a very long time to actually get used to the complicated user interface and also actually to learn the basic mechanics compared to most other games.
Graphics:
Every hero models are decently detailed. The spell effects are amazing as well. It is quite irrelevant since Dota 2 is not a game where graphics is what drives in gamers, it's more of the job of the gameplay to drive them in. Even then Dota 2 is an "easy on the eye" game.
Audio:
The audio in Dota 2 deserves a special mention. Valve has done an amazing job on developing the audio and speech of each hero. Each hero has numerous voice lines, most of them connecting a lot to their lore and personality. The voice lines of the heroes really makes the user feel more like being a part of the game than just being a player looking at a screen and pressing random buttons. The in game music is decent as well.
Lore:
The lore of the heroes are very well thought out. The way the story of each hero connects to another is really overwhelming. This adds a whole new level to the game experience. And as I mentioned before, the voice lines of the heroes represent the lore itself, so it really stands out.
Community:
Although Dota is notorious for having a intoxicant community, you would eventually come across really nice people once in a while. Playing the game and not winning can be very frustrating, and since it is an online game, it is common to find people who rage at others. But then again, think of it in this way: even if there is 10% ragers in the entire community, there is a very good chance that 1 out of 10 players in your game will be a rager. And it only requires one person to ruin the experience of all 10 players. And people can be really unsupportive when you are new. But then again, you should not label this as a shortcoming of the game itself since this is a community thing, not a developer thing.
Competitive Scene:
Dota 2 stands with the top competitive multiplayer games on the list. Well, I think most of you know this since the amount of Dota 2 tournaments going on every day is very high. Also, to add to this, the ability to watch the games from within the main game client is amazing. The spectator UI of this game is not bad either. Also Valve is known to host the biggest gaming event known as the International every year, where they invite the top Dota 2 teams to compete for a million dollars.
In conclusion, it's an amazing game with complex gameplay, decent graphics, amazing audio and lore. The only problem is to actually learn the game, given that there is a few "not so supportive" people in the community. It also has a ginormous competitive scene and excellent ways to interact with those competitive games. Although it takes up atleast a month or to just to learn the basics of the game, it is totally worth it once you actually learn to play the game in a proper way.