Both my parents and in-laws have been good grandparents. Not that I don't think there are things they could do better, especially as the kids have gotten older.
Three of my grandparents had died before I was born. The fourth died when I was in middle school, but she was never particularly grandmotherly. (My mother made lots of excuses for her, but looking back as an adult... she just didn't care to put in the effort. I don't think she was a particularly good mother either, but my mom still loved her.)
My parents (and my inlaws) do show interest in the kids -- they came to all the recitals/concerts, many of the sports games/meets, etc. They remember the kids on their birthdays. When the kids were younger, they tried to plan activities with them that they thought the kids would enjoy.
As the kids have gotten older, it's gotten tougher though. My mom has always been "opinionated" and she's not shy about sharing. When I was a teen, she was not shy about telling me if she thought my hairstyle looked terrible or if my outfit "did nothing for me." (The flip side is that if she gives you a compliment, you know she truly means it, but it's still hard.) When the kids were young, she didn't comment as much or the comments were directed at me. Now that they're older, she does it to them more -- giving her opinions (sometimes ill-informed opinions) about everything from their clothes, to their choice in music, to their friends. And they're all "good kids" with good friends. And they're not really boundary-pushing with their clothing and music choices either.
She's also gotten vocal with her political/social opinions and you never know what's going to "set her off" (avoiding controversial topics doesn't work -- although we do that -- because it could be something completely innocuous that sets her off on a tirade.)
I have tried to talk to her about it, but she doesn't seem to listen. She says "it's just my opinion. I'm entitled to my opinion." Yes, mom, you are... but you're ruining your relationship with your grandchildren. Is that what you want? THey still love her, but they walk on eggshells around her and I don't think they look forward to spending time with her like they used to.