I've ranted about this before here many times, so I'll try to keep it short.
The biggest culprits for the lacking performance of microwave cooking are lack of knowledge and "no metals in the microwave!" crap.
Sometimes you need some aluminum foil to shield stuff so it doesn't overcook, period end of sentence. If you don't know what you can and can't do with foil, roasting might be hard. Also, older microwaves with a stirrer fan and better wave guides (particularly before the bad stuff that has *only* a carrousel showed up) are less likely to self-destruct when used with foil than the cheapest trick on the block you can get new for a buck a dozen. With some particularly ill-designed microwaves you don't even need to use foil sometimes to cause trouble. We've used to live in an apartment that had a OTR microwave so badly built that if you had less than half a cup of liquid inside it it would just arc like crazy instead of making the liquid boil very quickly like other microwaves.
If you are *cooking* instead of just popping corn or rewarming leftovers, it pays to remember a few general things, which don't work exactly like this in *all* microwaves, but it's a good start:
(a) the center of the microwave is "cooler" than the middle -- if possible, arrange asymmetric food (like chicken drumsticks, for example) with the thinnest part inside the dish and the bulbous part facing the outside of the dish; if you alternate them instead to fit more, you'll need to pause the cooking at least once and reverse each item's position to get even cooking;
(b) whether or not you have a rotating carrousel, you'll probably need to stop the cooking at least once or twice and rotate the dish or stir the contents for best even cooking -- only microwaves with stirrer fans *and* a rotating carrousel might make this unnecessary; I find it funny that I have to mention this, because in the '70s, when nukers became affordable, people were amazed that they had to pay attention to the dish only once or twice and things were cooked *so fast* in less than 10 minutes compared to stirring constantly on the stovetop for 20 minutes, when now people are often appalled that they have to rotate and/or stir food once or twice and it takes *so freaking long* to cook at 5 minutes! ;-)
(c) just like you would never cook most dishes on a standard range burner using high power only, you usually do not want to set a dish on a 1200 W (or even 750W) microwave and let it go for a long time; that's why you have at least 3 different power levels (if not 10 or more) to use. It's very common to start a roast at one power and then switch midway thru and finish it;
(d) microwaves *can* brown roasts, particularly beef; it's just a question of using the proper timing and power; it's easy to make a meatloaf that is properly browned and delicious in a microwave in a fraction of the time it takes to make it in a standard oven;
(e) cakes can be moist and delicious, but you can't just make any single recipe and stick in there, even if they rise, they might become rubbery. For nice cakes from a microwave you need to use a recipe developed for baking in the microwave and such recipes will, in turn, fail miserably if you put them in a conventional oven;
(f) possibly the most important tip for microwave cooking: if you put a dish in for say, 1 minute, and then check it and it's halfway done, set the timer for 30 seconds next. If you are cooking one item for say, 5 minutes, and you want to cook 2 items, try 7:30 minutes *first*. You can always return the food to cook for another few seconds, but you can't undo "burnt". We are so used to regular burners and ovens taking proportionally longer that most people make the mistake of just doubling the time with microwaves. Most of the time you only need half of that, that's why it gets rubbery. It's not a miracle happening, it's that microwaves don't expose the food to cool air like regular cooking does, so you need less time;
(g) resting (or carry-over cooking) time is important -- if a recipe says for example, cook a meatloaf for 15 minutes and then rest for 5, it means that the outside inch or two of the food is at a much higher temperature than the inside, and the heat will transfer and finish cooking the inside in 5 minutes. If you check and find the middle uncooked and return it to the microwave without the resting time you risk overcooking or even burning the roast.
Anyway, there are plenty of yummy things that come off the microwave better than other methods. You can wrap corn on the cob or broccoli in saran wrap, for example, and in a minute or two it's steamed and ready.
Another thing to remember, it's much faster to cook some things (for example, a can of condensed milk, 3-6 minutes becomes a very nice caramel) than on a stovetop, but (1) some foods, like the caramel, might reach over 200F and you should be extremely careful with them and (2) they may expand 2-3 times their normal volume while cooking (they'll contract when cooling), for example, the can of condensed milk I just mentioned might need your largest pyrex dish to avoid overflowing while it bubbles and becomes caramel. DO NOT place the hot pyrex on say a granite-like countertop, use a trivet or potholder to avoid shattering the granite or pyrex, or melting/burning materials like Corian or Formica. I mention this because people are so used to quick stuff like warming coffee in the nuker and having the container on the cool side that they often don't think they'll need potholders and trivets when they are roasting, making a meatloaf or making caramels.
Good luck,
-- Paulo.
