Does the receiver have all the connections you need? Most modern electronics rely on HDMI cables to transfer audio and video signals, but many devices -- particularly older ones -- use other connections, such as optical or coaxial digital audio, component or composite video, S-video and analog (stereo or multichannel) audio. Take stock of your home theater and make sure that whichever receiver you buy can support your personal collection of electronics. If you have several HDMI devices, make sure the receiver has enough HDMI connections for your needs. Likewise, make sure you have the connectivity you need to support any older devices that you'll still be using.
Make sure it fits! Some of the more expensive receivers available are very bulky. Before you buy, measure your entertainment center to ensure the receiver you want can fit in its future home.
What features do you want? Oftentimes, the difference between two competing receivers lies solely in their feature sets. Almost all home theater receivers support HDMI's 3D and HDMI's audio return channel specification. Some new receivers sport an MHL-compatible (Mobile High-definition Link) HDMI input, which lets you connect certain devices directly, such as a Roku Streaming Stick. Some receivers will pass through 4K video; a few can upscale to that resolution (for those planning on buying a UHD TV). Networking features are big, including the ability to stream from the Internet (both Internet radio stations and providers like Pandora and Slacker). Most streaming-capable receivers will have Wi-Fi built in, but some cheap home theater receivers might require the purchase of an adapter to get wireless connectivity. Bluetooth makes streaming from a mobile device easier. AirPlay support gives you access to content on your iOS device (iPhone, iPad, iPod touch) and iTunes. Audiophiles will rarely be satisfied with automatic speaker setup programs, but for everyone else they simplify the task of making a home theater system sound terrific.
Do you want or need 7.1-channel audio? All 7.1- and 7.2-channel receivers let you add two back surround channels. Some (those equipped with Dolby Pro Logic IIz) let you use those channels instead to drive front-channel height or (in those receivers equipped with Audyssey DSX) front-channel wide speakers for a more immersive five-channel surround-sound field. But, before you decide that seven-channel sound of some type is a must, take stock of your listening room -- and how else it's being used -- to see if setting up seven speakers is practical or aesthetically desirable. Also keep in mind that relatively few Blu-ray Discs are recorded with any type of seven-channel sound, though receivers can simulate the extra channels from a standard five-channel surround-sound mix.
Do you need two subwoofers? Just about all home theater receivers have outputs for at least one powered subwoofer, but more and more are providing outputs for two -- that the .2 in a 7.2-channel home theater receiver. Adding a second subwoofer adds to the cost of your home theater system, but can provide better bass performance in certain listening situations. It's especially helpful in larger listening rooms and in setups with multiple seating positions.
Check the manufacturer's policy before buying online. Some manufacturers have strict policies regarding authorized dealers. Sony, for example, clearly warns prospective buyers that their warranty is not valid if they don't purchase their receiver from an authorized retailer. Some retailers offer their own warranties in such cases, but the decision on whether that's sufficient is one that should be carefully weighed.