I'm playing Dota 2, 'cause I can play nothing else on my laptop.

It's a game that teaches you the value of teamwork - and punishes you for its lacking. Working together is the only way to ensure victory. It's extremely rare that you'd be able to win the game on your own, and a five-man gank onto your poor ass will end up in blood and tears for you, no matter how many items you have.

That being said, it has quite a steep learning curve. To play effectively, you have to know all of the 113 heroes: what they do, what are their abilities, how to play them well (which lets you know how to play well against them) and even the quirks they have. You have to know the items, too: what to buy, what combines into what, what would be beneficial for this specific strategy (as there is no set way to play)... It may seem monumental, but it's this that gives Dota 2 a lot of depth. It's chess with 113 different pieces - and then some.

I've recently found a cool group of people to play with through voice chat, and it's been a completely different experience to playing with random match-made players. Ideally, you'd want this level of coordination and cooperation to persist in every game - using text chat, pre-made phrases activated through the chat wheel or hotkeys, or in-game voice chat. That doesn't always happen, because people play the game for different reasons and with different mindsets, not all of which aim at cooperation foremost. It's the reason Dota 2 is known to be "toxic", lacking as the word may be for description.

It's a fun game. If that's your kind of thing, you'll probably play it for a long time. It's free, and you can buy cosmetic additions - in-game music packs, HUD, hero outfits - from the official store or the Steam Marketplace. Be prepared to do lots of reading and lose lots of games to stupid mistakes if you want to be any good. Luckily, there are both the Gamepedia and the player-made in-game guides for heroes and various aspects of the game.