Everything you need and nothing you don't. Transmission includes critical features such as a block list function, global bandwidth limits, speed limits, NAT & manual port assignment, Remote desktop management, Seeding and Queue limits (I suggest stop seeding at ratio: 2.00 or a greater ratio) , and the ability to call a script when a download completes. In short, it works out of the box with little to no configuration, but has power and features should you want to set them/ utilize them.

Not officially available on Windows, but there is a port, making for a good app to use for those that use multiple OS's.