Livequartz is a good app, but no where near as all-encompassing as Photoshop (or even Pixelmator). I really dont like having to badmouth products, and I am by no means a pro, but I am very familiar with Photoshop, and theres really no comparisson at all.
For some straightforward things, Livequartz is good, and i believe if the development team just thought everything through a bit better, I wouldnt have to revert to PS EVERY TIME. They have seemingly neglected some of the most crucial and simple things, like being able to change the color of a shape after you drew it, which you cant do. There are always troubles with saving too, which is totally ridiculous.
Cant beat 5 bucks, but you really do get what you pay for.
Go for Pixelmator, its only 15 bucks and is definitely more comparable to PS.
I, for example, bought LiveQuartz first, and after maybe an hour bought Pixelmator. I never used Livequartz again. Youve been warned.