In fairness, this famous ring was Diana's choice not Kate's and it's the sort of engagement ring an excited 19 year old would choose.
I find it fascinating how onlookers often have such definite thoughts on it. Some don't like its provenance and wouldn't wear it at any price, and others call it 'ring of doom' and fated, cursed etc, while on the other hand some think it was a lovely gesture by William to choose to give it. Its mixed history has certainly divided opinions.
I don't mind it, as my own engagement ring has a large sapphire (and two diamonds) though not so huge as that one, and I love coloured stones. I agree it's not a practical ring at all, though. It resembles a dress ring in size.