It varies a lot based on the video - some are, in fact, just annoying. Mostly those that vary the beat too much, try to make you follow complicated patterns, etc. Also just the general quality, music and visual selection varies immensely. A poorly done one is worse than useless. So if the idea seems good but you're not liking it... might be worth browsing around a bit, try a variety of composers.

Also depends on mood; I wouldn't start an evening with one. Have to already be turned on and ready to gogogo, if you know what I mean.