Sure if you want to get really fat, this would be a great way to do it.

Not enough fiber and fat. Yes, you do need more fat (and different types of fat) than you think. Soylent based diets usually have enough fat. They still mess with your digestive system, though. I would use a diet like that only as an absolute last resort.

There's a product called Soylent that is intended for that. The creator said he did just fine for a few months, I think. But while there are some people who seem to hate food for some reason, others like astronauts and solders get the best food they can given their situations to keep moral up. I've heard soldiers say that getting good food is the highlight of their day. A ton of work goes into making the best food we can for them knowing that.

Food is meant to taste good but if you really had to, Soylent is what you're looking for to drink itself to stay alive. Ensure is a second bet but workout focused protein shakes aren't balanced enough to be your primary food source. Plus without fiber, you'll be pooping out your own stomach acid in a month... trust me.

What a disgusting thing to have to do.

A lot can depend on the total caloric intake. While it's feasible, it's not something that I'd recommend doing. A big concern could be in some of the B complex vitamins, as well as vitamin E and vitamin K1, which should not to be confused with potassium which uses the letter k on the periodic elemental chart, which vitamin K is important to the proper coagulation of the blood. The best source of vitamin K, is through the leafy green vegetables. Grains are NOT a good source of vitamin K. You also need to be sure you're getting enough copper, magnesium, selenium, and zinc, as those are some of the more common nutrients people can be low or even deficient in.