My MiL was kind, loving, funny and generous. Specifically (addressing some common MN complaints):
She adored her three sons but wasn't blind to their weaknesses.
She treated her three sons and DiLs exactly the same. No favourites.
She loved all her grandchildren and, again, treated them equally in terms of love (and indeed monetary value of presents etc).
She was very willing "emergency cover" for all of us but refused to babysit/childmind (because it exhausted her and, anyway, she couldn't offer an "equal service" for 6 grandchildren).
To "compensate" for not babysitting, she gave each couple £500 a year to pay for sitters!
If she had opinions about any of our parenting styles she bit her lip.
In other words she tried really hard never to do anything that could make her a contentious issue between sons and DiLs or between brothers or between SiLs. Best of all she was just great company who only proferred advice when it was asked for.
I know I was so lucky but I can't believe I'm the only one.