I have to say, everyone seems to be taking this whole thing way too personally and way too seriously.Adam did exactly what Maleena and Larissa both did - he followed his instincts. It may turn out, as it did with Maleena and Larissa, that his instincts were wrong, but I cannot fault him for following them. Do you really think that he would have been happier if he picked Rachel when he did not feel the same level of passion as he did for Samantha? I think that would be settling on Adam's part and not true to what his instincts were telling him. It may very well be one big booty call on Adam's part, but then again, he seemed a little bit more articulate about his feelings for Samantha than just saying "she's hot" all the time (although that's what everyone remebers most).
Adam also acknowledged that both he and Samantha would have to mature a great deal before they would be ready to take the next step, so he is not going into the relationship with his eyes closed. He knows what he wants, what he is ready for and what he is not ready to handle (like when he said goodbye to Brittany). It is likely that Rachel is far more mature than Adam is and that he would feel like he was dating his mother if he picked her. Dating someone that reminds you of your mother (not in a physical sense of course) is not a bad thing if you're ready for it. If you're not, it can be really weird.
Don't get me wrong. I would have dinged Samantha the minute I saw how she treated her dog (I love my miniature dachshund very much, but I'm not dressing her in anything, even if she would consent to wear clothing) and kept Amy and Rachel for the final two. But Adam said it best at the end of the show: he's the one who ultimately has to live with his decision - not his parents, not his friends and certainly not us.
I also think that it was fairly obvious that NBC edited the show to portray Samantha as the flashy shallow one and Rachel as the safe choice so as to make it even more shocking when he selected the girl who apparently everyone in America thinks was the wrong choice. I suspect that there is more to Samantha than was shown on TV (I thought that the butterfly tatoo story was nice - if it was true) and that Rachel has some shortcomings that we were not allowed to see. Adam probably got to know them a lot better than we did.
This relationship may go the way of Maleena's and (I think) Larissa's, but I personally hope it works out. Adam deserves to follow his instincts (or his heart or his little head or whatever) and be happy just like everyone else. If it doesn't work out - well, as Tennyson said, "'Tis better to have loved and lost than never to have loved at all."