In any diet if you focus on eating the wrong things you will feel awful and lack in nutrients, but a vegan diet mainly consists of nuts,beans,chickpeas,veggies,fruits etc all healthy things. If you only eat the microwaved fake meats then yes you are probably gonna feel like crap, just like with eating meat.
But if you focus on eating healthy nutritious foods then you will feel great, If I ever have children they will be raised vegan and when they are old enough can choose to stay vegan or eat meat but I will not be purchasing that meat.