I like my DH's sister very much (even though she has some annoying political views)- she's really nice and I'm glad we get along so well. I just wish we lived closer to each other so we could see each other more often.
My brother's wife (now ex-SIL, thank goodness), though? Never could really "get" her- and not because of a lack of trying. We just never became close- mainly because of her, not me. She is a really unemotional, non-demonstrative cold fish of a woman who never once showed any interest in trying to be friendly to me. My brother met her when I was only 12 years old, so I knew her for many, many years. I feel like I knew my other SIL better within a month of meeting her than I ever knew ex SIL. Now that she and my brother are divorced, I might never see her again, and I wouldn't be at all upset at the prospect.