TC, just be yourself and don't worry about a thing! I enjoy my MIL. She does get on my nerves sometimes, but she is older than my parents and is from the "bend over backward for my husband because he is the king of the house and must never lift a finger as long as I am alive to take care of him" generation. Both my inlaws are generous and nice. Once in a while she will ask some questions that I think are pretty nosy (how much does my husband make, how many bonuses does he get a year, what did our house cost, etc.) I would never dream of asking them how much they live off from retirement, what their house costs, etc. But other than that, they are just nice people. A little quircky, but still nice.
My own mother fits into the "scary" MIL mold. She is always giving out unsolicited advice, will never say, "Gee your house looks great like it is." She's always over saying things like "Why don't you move this over here? Why did you decorate like that? Why would you pick this color? Not to mention the look of disgust on her face when she says these things... The cup isn't even close to being half empty with her, it's almost always bone dry. She is jealous of my brother, my sister and me (none of us have kids, we all have houses and we have comfortable lifestyles). Meanwhile, SHE had three children by the time she was 28, never had two pennies to rub together, etc. etc. Hello? Can you be happy that your children have successful lives?
She always told me to elope - so when I got engaged, that's what we planned to do. When she kept pressing us for a wedding date we confessed our plan. She stopped talking to me. I had to invite her and my father to the court house then! My husband's friends kind of knew when we planned to elope, so they thew us a surprise shower! I was so touched and completely blown away. When the shower was over, I called my mother to share the good news. I was a bit surprised she wasn't at the shower, but figured she felt like she might have been the oldest person there. Nope. Turns out she was invited but didn't go because "I didn't deserve it." In her mind it was wrong for me to accept gifts from these people (who by the way planned the surprise shower, didn't ask me if I wanted one...) They were obviously happy that my husband and I were getting married and they just wanted to show their love and appreciation for our friendship. And I didn't deserve it - because there was no "wedding". Ok, so you are supposed to have a wedding just to get gifts?
I could go on and on...