I don't like their stance on homosexuality, or their treatment of women. Some sects are better than others, of course, but in general, that's my beef.
that and,
marriage to dogma
exclusivity of many of the groups
propositions of absolute morality and inability to be flexible in society
distrust and friction against science and biological advancements
seeing war and violence as a tool of Gods will
viewing crimes against humanity by holy groups as reasonable (pedophile priests for example) or unavoidable
belief that problems of society are man to blame and accomplishments are God's "gift" --giving humanity very little or no credit for its own advancement
presenting a fictionalized view that there is no such thing as death (for believers)
the "carrot and the stick" mentality of believe and be saved don't and burn for all eternity
The elevation of faith as a supreme reality that trumps evidence when the two make contradictory claims.
the belief that the 2nd coming will be a glorious thing even though it involves the destruction of the world.
That pretty well sums up my objections, but I'd elaborate, under "marriage to dogma," the almost universal belief among Christians that it's very important to believe certain things that later people (not Jesus himself) taught
about Jesus, but not at all important to follow the teachings of Jesus. That is, Christians will say, if asked, that it's important to follow his teachings, but then they immediately begin to explain why it's not wise or desirable to do so. The actual teachings of Jesus are completely superfluous to Christian thought.
Also, I completely despise (and I did when I was a Christian, too) this Evangelical nonsense about "accepting Jesus as your personal savior" and "having a personal relationship with Jesus," which is completely unscriptural and unprecedented in Christian history at least until the great tragedy of errors we call Dispensationalism came along. Unfortunately, Dispensationalism has been so aggressively promoted that this kind of thing, along with sheer lunacy about "Bible prophecy," has become common, not only in marginal sects but even in the historic churches.