I don't play with mods but i played like 10 songs with HD just now and i can say that the song rhythm makes more sense with HD on. I am sure that if i got used to HD i would prefer it over no mod by a long shot. + it actually makes map look easier, dunno why D: .
EDIT: The thing i do not like about HD is when a song goes silent on vocals/beats and there is only the background instruments playing or effects then you are practically left on ice and the only way to hit notes correctly is by basing them off of the previous rhythm (but you DO you have to remember it to hit 300's and that will take time to get used to i guess). So technically while you are remembering note positions some times you also have to memorize the song rhythm pattern in order to correctly hit some parts.
EDIT: The thing i do not like about HD is when a song goes silent on vocals/beats and there is only the background instruments playing or effects then you are practically left on ice and the only way to hit notes correctly is by basing them off of the previous rhythm (but you DO you have to remember it to hit 300's and that will take time to get used to i guess). So technically while you are remembering note positions some times you also have to memorize the song rhythm pattern in order to correctly hit some parts.