What defines a good keyboard? Basically, just the switches. Of course there's an overall build quality and various features like media keys. But the switches create the tactile feedback that your mind uses to process the act of typing. Without it, you can't tell if you pressed a key or just remember the muscle movement of pressing that key. It's weird, and it's science.
You know the loud, strong clack of a Point-Of-Sale computer's keyboard? Think of Sears or JC Penny's checkout computers from the late 80's that are still in use or recently retired. Those keyboards were loud and the cashier seemingly mashed them. Well, that's because of all the key switches, those have the highest actuation force.
How do you figure all of this out? Switches are categorized into colors.
Blue is the most common clicky switch, it's purposely louder than most switches and provides good tactile feedback as well. It's popular for typists but unpopular for gamers because the release point is above the actuation point and thus requires more energy to double-tap than other keys. Red switches have a low actuation force and medium tactile and audible feedback making them good for gaming. Black is the Point-Of-Sale switch as its designed to minimize typos by requiring good force for a high distance. They're poor for typists and gamers, but good for those with disabilities or cashiers. That's not an insult to cashiers, mind you they type quickly while standing. People with disabilities such as Parkinson's benefit from keys that are difficult to accidentally press. Brown is my favorite switch, it provides strong tactile feedback with minimal audible feedback. The switch is designed for both gamers and typists, and can be used in an office environment without annoying your coworkers with clacking.
Visit my Computer Store for recommended keyboards of various switches and features.