I did drain some of the liquid from my canned diced tomatoes (which included garlic and onion) and added more seasoning, as recommended. Also, I didn't mix the spinach, mushrooms and zucchini into the ricotta; I just layered them between the ricotta and sauce. Other than that, I followed the recipe and it was delicious! No soupy bottom for me, and the veggies were crisp-tender. I was very skeptical, but it does cook beautifully.
On a side note, I prefer to use my slow cooker on weekdays so I come home from work to a hot meal. This recipe, while effective, has a relatively short cook time so I can't make it while at work. It did come in handy as a summer meal when I didn't want to use the oven.