One of the best things in CCS for me are the little lovey-dovey moments all the time (so cute!) Nelvana got rid of so many of those moments! Yeah sure they kept in many of the s+s moments, but what about Touya and Yukito? Theyre a very cute couple and I think Nelvana edited all of that out, plus Tomoyo's admirations of Sakura. *cry* Those people massacred the series.
Plus, the voices don't suit.
*EDIT: I almost forgot, the music in the english version is kinda, slightly....cringeworthy.