Plant-based diets are usually superior, health-wise, to meat-based diets.
There are a couple of nutrients that vegan diets at one point may have fell short in, like B12 and D being common examples, but at this point those are present in fortified vegan milks or breads.
The only other ones I can think of off the top of my head are a fatty acid present in fish, that is easily supplemented. Or less essential nutrients like taurine, which are also easily supplemented if one finds that they really need higher levels.