I tried ketosoy for a week, and will likely continue... but I only replaced about half my intake each day with it. I have trouble getting 20oz of it down at once, so tend to break into 4-16oz portions... doing roughly half a pack a day combined with a real lunch or dinner and one snack (nuts, apple, etc) through the day. It actually worked out pretty well.
While I try to eat relatively nutritionally balanced, I'm not perfect. I have a broken metabolism, and chronically bad knees. This makes exercise difficult to say the least, and whatever I eat will have an effect. What it did allow me to do was consistently stay under 2000-2400 calories a day, and actually drop a little bit of weight.
I'm planning on getting a gastric sleeve later in the year, which will make something like soylent ideal for me.
That said, I love to cook and usually do at least one longer prep meal a week (friday, saturday and/or sunday)... This past saturday I made mushroom broth, followed by an asian-style soba (buckwheat) noodle soup using some of said broth with thinly sliced sirloin and veggies.
So, I can really see both sides of this. On the one hand, I love food. I try 2-3 new to me restaurants a month, and like to take lunch away from my desk. On the other, sometimes just drinking something down is far easier than taking the time to prepare a meal. I've been making several gallons of stock/broth every other week for soup for most of the past year. It takes quite a bit of time and even only doing it a day or two a week, not doing it for half my meals appeals to me. And will often cost less.