Especially since the almost-as-large and far lighter 737-900 has come along
There's nearly 30,000Kg's difference in the max take off weight between the B739 and the B752! Whilst it might take almost as many pax, it may not take all their baggage, or take them nearly as far!
The B757 was originally designed to be a 2-engine, 2 crew replacement for the B727 and was to be able to fly coast-to-coast America. It's versatility made it very popular, and it soon got ETOPS approval and was adopted by many airlines.
Versatility wise there is no other option - it can lift 115,000KGs, fly for 7+ hours, is great hot & high, and is so over-powered it's a dream. Add great brakes and there really is no other airliner like it. It's also by far the best looking airliner - everything is in proportion and winglets really finish it off.
And yes, I am very biased and very privileged as it is my place of work!