I like my microwave, but it doesn't do everything, or even everything people tell you it will do - but neither does a frying pan or a kettle, everything gets talked up. I'd definitely replace it immediately if it died on me
Mine is a combination oven which is good for some things, but we will assume just a basic, simple microwave. I am however using it on dual function or as a small low energy oven more and more
First, and most obviously it is great for defrosting and reheating - I am mainly feeding a single person, and it is really handy to have things like chili in the freezer which certainly can be defrosted and reheated in minutes, arguably even better than messing about remembering to take them out and let them thaw in the fridge or at room temperature I think some things do cook well in a microwave, could sum it up as moderate amounts of thing that steam well - vegetables, fish, rice preferably in a microwave rice/veg steamer, it's not much quicker than on the hob, but for a small amount, one or two portion it gives a better result in my opinion
The other thing I use it for is prepping ingredients when cooking - softening butter, melting chocolate etc
It's also a great cat proof food safe if you are leaving something to come to room temperature!