My first reaction when I saw the game "League of Legends" was "lol". A game called LoL? It mustn't take itself too seriously, or be that great of a game. But once you get past its glaring flaws, LoL is a really enjoyable game especially when you consider the cost -- free.
To play the game, you choose one of 40+ "champions". There are 10 different free-to-play ones every week, or you can use "influence points" (earned by playing games) or "Riot Points" (purchased with real-world money) to buy a champion and have it available to play any time you choose. The sheer amount of champions guarantees there is at least ONE champion you'll enjoy playing, and when the game becomes boring you can switch it up by trying a new champion. Having so many champions poses difficulties though, because you have to learn to counter so many different opponents.
It's really easy to pick up on the game, especially with the tutorials available. To master the game, takes a LONG time however. Small decisions can make or break a game, and team cooperation is key (see: community). Somehow, even though every game is "the same" -- on the same map, with the same objectives -- every game is different and interesting.
The game can be played in 3v3, 5v5, or practice mode (with AI bots). 5v5 is the most popular, and the map is larger and games usually take longer than in 3v3. You can queue up with friends in an arranged team, or you can solo-queue and hope you're lucky. You can also play ranked matches if you want some street cred on the LoL forums, or just to feel good about yourself.
The community of players (called "summoners") is one of the worst I have ever seen in any MMO. Players begin to berate you before you even step foot on the playing field. There's also no username-filter, so many of the summoners' names are extremely offensive, but no worse than the insults and slurs you'll hear strewn in most every game you play. I've also come across religious nuts who said the only reason we won a game was because it was the "will of God". I don't recommend playing this game if you nerdrage easily.
Even if you do get a good group of people, you run a very high risk of having someone on your team or the opposing team AFK or nerdrage and refuse to play, or just plain disconnect. I couldn't give you an exact number, but I'd say it's definitely upwards of 25% of the games that gameplay is interrupted because of a disconnecting/AFK player.
Updates and Cost
Riot releases new champions or new skins every week, which keeps the content fresh. You can purchase skins and champions with real-world money using "Riot Points". It's a way for the company to make money, and I have personally supported the company in this way, but almost all the game content is free.
One glaring problem with the game is its server stability. It seems as though every day the server goes down for an extended period. Many say we don't have a right to complain because we aren't paying for the service, but I disagree. Riot HAS stated that server stability is their number one priority though, so I can only hope that the problem is lessened in the future.
The client seems relatively stable and I've not had any major issues, or bugs. The client, like most games, is a memory-hog, and is pretty graphics-intensive considering its graphics aren't really that in-depth.
At the time of writing, there is not a Mac client. There is one in beta-testing however.
All-in-all, this is a worthwhile game to try if you enjoy strategy games such as Warcraft III or Starcraft. t's free so you might as well. So give it a try -- that is, if the servers are online and you can actually log in.