Why use a micro-transaction model in the first place?
Developer benefits:
- Developers don't have to spend years developing new systems - the core of the game is already out there, and they can publish more content for it.
- Consumers continue playing your game: why switch games when your favorite game is still new and exciting?
- Stifles competition: consumers would rather spend $10 for new content on a game they love rather than spend $60 on a game they might love.
- Revenue increase: consumers are more willing to spend money if it's in small increments. They'll say "Oh, it's only $10!" for the 20th time.
- Micro-transactions provide a steady flow of income rather than a big burst of income. This keeps a company going while they develop another game.
- Word of mouth: because consumers play your game for longer periods of time, they will likely talk about it, therefor continuing a cycle of new players rather than growing stagnant.
- Longevity: you are able to continue playing new content for a game you enjoy.
- Smaller cost burden: instead of spending big chunks of money at a time, you can manage it across a longer period.
- Constant updates: because of the nature of micro-transactions, you know the company is going to continue updating your game, fixing bugs and problems instead of just calling it a finished product.
- Free to play: most micro-transaction games include a free to play option. Whether it's an MMO like LotRO or an Action-RPG like League of Legends, you can still continue playing your game or trying new games even during low-budget times.
- Easy to play with your friends: because of the lack of a cost barrier, you are able to play with your friends easier. All they have to do is download the client and go!
Micro-Transactions across the genres
Now you may say: "well, micro-transactions wouldn't work in x genre!" False, my friend! Here's a few examples for ya:
Shooters: First-Person or Third-Person
Bungie got micro-transactions right. Starting with Halo 2, they started releasing map packs with new online content. These generated a massive amount of income, and showed one of the easier ways to keep players coming.
Borderlands has done great as well. Starting with The Zombie Island of Dr. Ned and continued especially in Secret Armory of General Gnoxx and the Claptrap Revolution, Gearbox knows what it's doing.
Other good examples would be including new modes: many FPS's have offered DLC similar to Halo: ODST's FireFight or Gears of War 2's Horde Mode.
Role-Playing games
As mentioned above with Borderlands, RPGS can offer a wide variety of DLC that interests the player. One simply has to look at BioWare and it's wildly successful Mass Effect 2 and Dragon Age: Origins DLC's to see micro-transactions at work.
Extending the story-line, increasing the level cap, and offering great sidequests will keep people from leaving their favorite RPGs.
Strategy games - Real-Time or Turn-Based
TBS and RTS generally don't use micro-transactions to extend their game, rather relying on expansion packs that offer new single-player content and a few new multi-player maps and units. However, spreading that out across a series of DLC's would work as well.
Imagine, instead, that Starcraft 2: Heart of the Swarm would be a series of DLC's. Instead of charging $60 for the single player campaign and a few new units in multiplayer, why not offer players who already have Wings of Liberty who don't want the single player campaign the option to purchase the extra online units for $15.
Or, alternatively, offer those who want to play the Heart of the Swarm campaign the option to buy the maps as they are finished. Imagine that the first 5 missions were released in November for $15, the next 5 were released in February for $15, the next 5 were released in June for $15, and the last 5 were released on the same day as the retail game for $15. Then, if you purchased them all individually, you get the online units for free.
This time of situation keeps players at the edge of their seat, salivating for more Starcraft 2. They talk about it with their friends, generating word of mouth. They keep playing the game, so that when the next pack does come around, they are already eagerly awaiting and purchase the pack immediately.
Music-based games
Do I really need to even say anything here? Rock Band DLC - 'nuff said.
Micro-transactions will be used in almost every game in the future. It's the new way of distributing games and their content, and Riot's League of Legends shows just how wildly successful and profitable the idea is.