DoTA (or Defense of the Ancients) is a game belonging to the MoBA genre (Multiplayer Online Battle Arena). The games starts with 5 players on a side, each player controlling one character. Also, every team has an "ancient" which is a structure which is heavily guarded. The aim is to destroy the other teams ancient and the team doing so wins the game. However, it is not so easy to just go ahead and destroy the ancient. There is line of towers that will deal heavy damage to you on your way to their base, where the guarded ancient is. You need to level up your hero and get more gold, with which you can buy items which will give your hero damage, survivability or simply an advantage in team battles. Killing your opponents heroes from time to time is also important because if their character becomes overpowered, it'll later on be impossible for you to advance to their base or to guard your own base.

DoTA is a highly strategic game wherein you don't just take the most overpowered heroes and go ahead with the game. If everyone did that, your team is going to lose. You always pick a hero who will keep on collecting gold and levels most of the early game only to come in late game dealing a crazy amount of damage and be more or less invincible. This is called the "carry" of your team (you may have more than one carry, or a mix of carries and semi-carries). Then you have supports, whose job is to help the carry become overpowered. Their job is to give their team a strategic advantage by planting wards across the map which gives vision of certain areas of the map and buying support items, items which can heal, or disable a person of the other team, or simple give a boost to all other players within an area, which is extremely crucial in team battles. Supports are expected to not collect gold from kills or last hits, but instead give it to their carry if he is around. Each battle lasts for no more than 12-15 seconds in the extreme case and the winner is determined on a lot of factors including how the order in which the skills were used, how did a combination overpower the other heroes (for instance a skill that increases magic damage combined with a skill that deals a lot of magic damage), your knowledge of where the heroes are on the map, how you entered into the battle, etc. The items you buy also greatly depend on the heroes in your team and the heroes in another team (for ex., if the other team has a lot of people with a lot of magical skills, go ahead and buy an item that gives you magic immunity). There is no "one-size-fits-all" inventory in DoTA 2.

Team battles often become deciders of a game because their always is a huge shift of gold and exp whenever a team battle occurs. Team battles aren't pre-announced or pre-determined by the game. You are just roaming around the map, find someone and there might be a team battle, or you may strategically be roaming around the map looking for the other team to hunt them down and kill them.

PS: The last tournament which happened for this game, conducted by Valve, was 'The International 3', which had a total prize pool of 2.7 million USD.

It's an RTS/RPG hybrid. A standard top down view strategy map with two opposing bases, with tiered fortifications. Each base is already generated at the beginning of a match and automatically creates computer controlled units and sends them to battle. The human player is a single hero trying to affect the outcome of that battle.

10 players make up two teams (5v5). They each begin the game as weak lvl 1 heroes. Initially the focus is on killing the computer controlled units (creeps) to gain experience and gold for items. As the hero gains levels and items they are able to do greater amounts of damage to the opposing creeps and opposing human controlled heroes. At high level heroes will destroy entire creep armies and siege base defenses. The game is won by destroying a primary building at the base of the opposing side.

What makes it fun/compelling to me.

Games are short with no character permanence. No standard RPG style grinding. Just a 30-45min RTS style chessmatch

Minimal wrote build orders. Unlike the first 10mins of most RTS matches

Controlling a single unit lessens the clickfest aspect of most RTS style games

Coordinated teamplay is vital, but this can also result in new players getting flamed mercilessly

Beginning with a full base with defenses and creeps by default prevents the standard RTS formula of rush > boom > turtle > rush. Opens up more options for gameplay and strategic depth. Dota is designed in such a way that games tend to explode rather than stalemate. Hero HP is additive, but damage is multiplicative (avoiding games that drag on despite being over).

It's a five on five game where you are trying to destroy your opponents base. Each player selects a character to control, those characters grow stronger over time. The game is won by properly anticipating your opponents strategy and preventing them from anticipating yours. There is also a high skill ceiling for controlling individual units, so individual players can be a major help or hindrance to their team.

Its a MOBA/aRTS (depending on what category you want to call it), where 2 teams of 5 players control characters trying to destroy the opposing team's buildings. (more at http://en.wikipedia.org/wiki/Dota_2)

There is an official Linux client but I wouldn't recommend it unless you want to lose a lot of free time as the game takes over your life. ;)

It runs natively on linux, it's free and bugs, but not source code, are hosted on github.

I really recommend watching this http://m.youtube.com/watch?v=UjZYMI1zB9s just make some popcorn before.

If you're a bit more curious but don't want to get the game and try it out, Valve made an excellent documentary [1] that gives an introduction to the game and shows why it's so incredibly compelling.

[1]: http://www.freetoplaythemovie.com/

This is a video of one of the in-game tutorials (the tutorial is rendered in-game, with the same camera perspective as a player), it does a decent job of explaining the game: https://www.youtube.com/watch?v=zmRBvla8tSY