Throughout my cooking life, I have had a love/hate relationship with slow cookers. Even with the help of two slow cooker cookbooks, I have never been bowled over by anything that comes out of a slow cooker. It seems to me that they are best used for keeping soups, stews, and chilis hot on a buffet.
I think my biggest problem with Crock-Pots (and I use that term to mean all plug-in slow cookers) is that when cooking meats, to get the best results, you have to brown it in a separate pan first then transfer it to the Crock-Pot and add the remaining ingredients. Those looking for a mess-free short cut to cooking (me) now have to deal with a crusted pan and a splattered stove, and that totally defeats the purpose for me.
Two recipes that I do think work really well in a slow cooker are chicken breasts that are cooked with a little water and then shredded to use in tacos or enchiladas (they do stay moist this way), and chile verde also made with chicken.
I have owned slow-cookers and always ended up giving them away. Here's what I do instead.