The Mazda6 has been sold with I4 and V6 engines. In some markets, a diesel I4 engine is offered. Those engines have been paired with 5 speed automatic and manual transmissions in early models and 6 speed automatic and manuals in later models.
The Mazda6 has been sold with front wheel drive and optional four wheel drive.
There is a performance version of this car sold since 2006. It's called the Mazdaspeed6 and it has a turbocharged engine. The North American version of that engine makes 274 horsepower. This car is intended to compete in the same market as the Subaru WRX STi and Mitsubishi Lancer Evolution. It also has several luxury items standard that are optional or not available on the standard Mazda6 model.
These cars can be found on the used car market. They keep their value fairly well, so look to spend more on one of these cars than you would for a Chevy or Ford from the same year. Look on eBay for some really good deals and hundreds of listings for aftermarket parts.