I'm not really a Christian, I guess...and I'm not sure I can answer the question. I used to be one, and possibly, tossed much of it for the reasons you bring up, Tater.
That said, I don't need to think about original sin or "redemption" (in the sacrificial Christ/forgiveness of sins sense) to see the worth of some of it. If I lived in his time, I would have been challenged to follow Jesus anyways because of the Sermon on the Mount alone. Granted, his ethics are not unique (many others have precepts like the Golden Rule, warnings against hypocrisy, etc), but it's still worth following either way. If Christianity gets more complicated than that.. if it emphasizes theology, sacrifice, or anything Pauline, then I'm all "meh" about the whole thing.
Also, I resent Christians who do emphasize these things.. who basically like skipping past the life of Jesus, and shifting the subject to Christ, the dying Son of God.. that whole deal doesn't make any sense to me. Ethics matter. Sacrifice and dying for "humanity's original sin" - not so much.
I've heard many sermons that even say "It's not good enough to be a nice person. You must accept Jesus as your Lord and Savior. Then God will look kindly on you." I disagree and find it highly insulting. And I defy a God who is incapable of looking kindly on nice people, who eschews good behavior, and instead, demands sacrifice and blood to forgive them....because of vicarious "original sin". An idea based on a completely fabricated story that demands you believe an "Adam and Eve" existed 6,000 yrs ago, and were the first human beings. That is far too challenging...and unjust.
My belief is that being nice is really the only thing that matters. And if we talk about "heaven", I prefer that passage that Christ himself said: "The kingdom of God is within you." If he actually said that, then he did NOT believe in original sin (for then how he could make that kind of appeal to inner-light and goodness in people? If people are that tarnished, then he would have never dug that deep and saw potential). It's a passage that tells me that whatever better world we're looking for is neither here nor there. It's in you. It's telling us that the present matters.. that trying to make this place a better world matters..that people can start fixing things now if they have the courage. It's not easy, but this works for me...instead of switching one's emphasis on the future, on death and afterlife, on emphasizing that we're completely broken, on saying "God will eventually save you when you die if you're but cleansed". This are Pauline ideals, not Jesus ones per se. In my mind, Jesus was trying to inspire change, not redemption. There's nothing to "forgive" or be jaded about. Only one Gospel is bent on redemption and Cristology (John) - it's also the latest dated one. And one written in an anachronistic, interpretive style.. which makes me take it less seriously on giving any indication on what the "human" Jesus might have been like.