Slow cookers are great for all people, from lazy people to people that like to make fancy things.
For lazy people, the general rule of thumb is "you put sh*t in and food comes out". A few good starter lazy crockpot recipes? Black beans and rice and taco casserole. Also barbecue tofu. Also sweet potatoes, if you're heading to a potluck type of dinner.
For people who work late, crockpots let you do almost all of the legwork for a really great meal, but you can do it the night before or the morning of. This was great for days I didn't have to be on campus until noon, but had class until 7 or 8pm. The truth about crockpots is that you do need to do some prep work, at least for a lot of the really good meals - you should soften the onions and garlic, etc. But the great thing about a slow cooker is that it lets you do all that work at 9pm the night before, and then do all of the dishes, and then the next day you have a great day and a clean kitchen. If you get into a good cycle with this, dinner is eaten and then dinner is cooked - it avoids rush-job dinners or reaching for the phone to dial out for pizza. Some good recipes to try out? Fish in foil or sweet potato barley risotto.
For vegetarians, crockpots are a great way to cook a lot of vegetables together, and also to try new things. I learned to like curry from my crockpot. Sweet potato tacos? Would have been totally weird to me, but I love them. I also love sweet and sour tofu in the crockpot. Chili with Seitan? Never would have tried without a crockpot. Since vegetarian meat substitutes tend to be pretty tasteless, the crockpot lets these substitutes absorb the flavors in the dish over time, which is awesome.
For people who like good food, the argument is that a crockpot lets you buy things like cheaper cuts of meat and do good things to them. It also lets you make really good dishes that seem fancy but are made with cheap ingredients.
For people who work from home, there is nonetheless an argument for the slow cooker. I love the slow cooker because it lets me take care of dinner in the middle of the day, or in the morning, and then I don't have to worry about starting it later, and more importantly, because the crockpot doesn't burn stuff or leave things on the burner just a little too long or forget to preheat the oven. Once you get the hang of crockpot cooking, pretty much everything comes out pretty darn good. The crockpot doesn't let you use starting dinner at 3pm as an excuse for not getting work done. It also lets you make a nice dinner without having to stir the pot constantly.
For example, tonight I made leek and potato soup on the stove. I would have rather done it in the crockpot, but I started cooking around 3. I'll share the recipe in a separate post, but I will say that I was constantly fussing over my soup and making sure it wasn't boiling over - not really a concern in a crockpot. When I caramelize onions, I don't have to worry about them burning. So if you've written your crockpot off already, dust it off and give it another chance.