What Ankur said is the first thing to look out for. Matrix Metering Mode should
be sufficient in such cases.
In case it is not (it should be palpable right by looking at your shot even in the camera LCD), try switching to "partial metering" and then take Big Ben into focus. Camera will try to expose correctly for Big Ben and leave the other stuff out while metering. Later in Lightroom, boost the shadows.
In the photo you have posted, I can see lack of contrast as well. Try bumping it up in Lightroom.
Lastly, I've seen difference of day and night when you use a quality lens for night shots. Do one thing for me, next time, from the same place, take one photo with your 18-55 lens and the other from 50mm prime. And let's see the difference.
, I am trying to separate two things here, both fall under "Long Exposure" category however what Santosh pointed out in my case is a "night shot" whereas what you posted later is probably a "dusk/dawn" shot.
While what Ankur said about Manual Blending can be 100% correct, I personally don't do blending for night shots. The key here is "night". Dusk shots or Dawn shots definitely show up better with blending, however I personally don't like the affect blending has on the night shots.
The Oprah house photo that you liked is also take with a prime. So when we are at primes and Ankur has kicked off the streak for "Long Exposure Dusk/Dawn" shots, here is another favourite of mine. This is again a single shot with long exposure achieved through a filter.