We stayed at the Imperial at the end of August. After reading some of the comments here, I was very concerned about our stay. We were totally WOWED by the Imperial and I would definitely return there in the future. Some standouts for me....
the hallways, filled with Indian prints and artwork
the pool is drop-dead gorgeous and a fantastic place to unwind at the end of the day
great little bookstore with unusual and older titles
breakfast was top-notch with numerous flavors of lassis, and great baked goods. One of my favorite breakfasts anywhere.

And the rooms are fantastic too. The rooms, to me, seem a little closed in due to the architecture of the hotel, which includes very narrow windows. But the housekeeping standards were very high. The room attendant took a very proprietary interest in the room, and was always responsive to any of our needs or requests.

The service at the Imperial was really great. In particular, the concierge got us an incredible tour guide with less than an hour's notice, and the guy only charged about $20 for four hours. It was a steal, and we did leave a very big tip. Also, we were truly satisfied with every driver we got through the hotel. Some were better than others, but they were all good, and the car service was quick and reliable.

I stayed in the Oberoi last time I was in Delhi, but it has nothing on the Imperial. I love historic old hotels (Raffles in Singapore being a favorite), but only if they have been maintained to a very high standard. The Imperial didn't let me down.