it really depends on what you do. i will first DISCLAIM that no app or collection of apps has the breadth of features a program like photoshop has on an ipad. illustrator hasn't even really been touched, there are a few apps that nip at it's heels, but both these programs are so large with features, the ipad is still playing catch up. indesign? forget about it.
however, most of my personal/professional use of photoshop is for digital illustration and painting. for that specific niche, the ipad app, Procreate, fills my needs ENTIRELY. it is, in fact, WONDERFUL. i'm amazed at the attention to detail the app has. even little cheats and tricks i used to use in photoshop show up in this app and some that photoshop can't even do (perspective assist). but, again, that's just for me and my use. it depends on what your workflow is. you may be able to get by, but i feel like you'll be saying, "oh this was so easy to do in [insertapphere]!!" often.