Well, the use of colors in the show is quite-bland, but its actual animation is actually MUCH better than most shounen shows of today (going by actual "movement" being what i consider to be "animation"). The fight scenes are usually really fluid, and the artwork may not be to most people's liking, but it certainly gives the series a unique feeling that prevents it from ever feeling like any other generic shounen series.
Overall, I like HXH, but I do agree that its not nearly as interesting as YYH (IMO).
Personally, I find that the thing about YYH's high-quality characterization is that its just so damn good that it completely makes me forget that I'm watching a really old anime with low-quality animation. To me, that's the mark of a brilliantly-made show, personally.