Slow-cooker recipes can be a crapshoot for me - even from the same author (for instance, I tend to have good results from Michele Scicoline's French Slow Cooker book, but not so much from her Italian Slow Cooker book.) In general I find the following to be true:
- Recipes with too many liquids tend to be super bland. Some of the best ones I've made had barely any liquid at all, and allowed the meat and vegetables to give off the bulk of the fat/moisture needed. (Great example: this recipe for Bargemen's beef stew where basically all the cooking liquid is thrown off from the onions at the bottom of the cooker.) So cut back on the stock/water in a stew recipe if possible.
- Browning meat is (nearly) essential. It does seem to defeat the purpose of throwing-it-all-in-a-pot-and-forgetting it, but most roasts and stews will really come out best if browned first to lock in the seasonings (and be sure to season them well).
- Related to the above, a lot of the time I'll brown my meat and throw all the ingredients together in a plastic bag the night before, then dump it all in the slow-cooker before I go to work the next day. That seems to end up giving me more tender/flavorful meat since it has time to marinate.