Hard at the beginning, but once you pour souls into the stats you want and have the correct weapons it's a breeze. Currently on NG + 10 and the bosses I only struggle with is twin princes and pontiff. Other than that I use a hidden body spell to run through the game and keep doing NG+ to get five free levels every time from the guy who gives you a dark sigil. Use this website if you need help: https://lfg.pub/g/dark-souls-3