I got the card in the mid/late 1990s. A co-worker said it was the best credit card out there, for people who care about points accrual, and he was right.

Acceptance wasn't great, but for T&E it was fine. I think most/all the airlines, hotels, and expensive restaurants took it. Other places, not so much.
The weird denomination ($1,000 of spend = 2,000 points, and 2,000 points = 1,000 miles) went away when Citi sold it.
Other things I remember about it:
- You had 60 days to pay the bill. When I first got the card, I think I incurred about $12,000 of expenses prior to my first required payment before they finally declined a transaction
- Pretty much all airlines participated (like SPG today), so much better than Amex in terms of airline partners
- You could convert American and United miles back into Diners Club points (there may have been another airline as well). 1,000 AA or UA miles = 1,000 DC points, so you kept half their value
- British Airways regularly ran promos, for a few months at a time, a number of years in a row, where the exchange rate was 2x: 1,000 DC = 1,000 BA miles. So $1 of spend became 2 BA miles, and during this time, you could convert (in increments of 1,000 miles) your AA and UA miles to BA miles at 1:1

I got to fly the Concorde on BA a few times thanks to DC and the BA promo conversion rates.

One year, I paid the $300 annual fee and got the "Carte Blanche" version of the card. I didn't end up using any of the benefits, so I switched back to regular DC the following year.

And here it is, Year 2018, and I still receive paper statements and I have no idea how (or whether it is even possible) to turn them off.

It is the red-headed stepchild of credit cards.