Home intercom systems are not what they used to be. There was a time when having one meant you could pipe music through the house, check to hear if the baby is awake, and tell the kids to come to dinner without having to go look for them. Well now they offer features that let you monitor rooms inside your home, all over your property, both with audio and/or video, plus all the things they used to have.
The first thing you need to figure out is how much you can afford to spend. Then decide if you want a wired or a wireless system. Voice only systems are adequate for the average needs of a homeowner, and are less expensive than the video intercom systems. However, if you have a locked gate surrounding a large property, being able to see who is asking for entrance is a good thing! And if you employ servants, it is helpful for them to see who is at the door or gate before allowing them to enter.
Do you need a connection to every room in the house or do you just want them at your entrances and in the master bedroom? Perhaps you want connections between your room and those of the children. Get detailed information about warranties, installation, and service contracts. You need to know that there is good customer support to fall back on as you are learning the intricacies of your system.
If you can afford it, and you have kids, video is a good thing to have. Teach them to never open a gate or door if they do not recognize the person on the camera.