Valhalla Room is a great reverb....its strength, as bitflipper said, is the long, lush verb...I use Valhalla Room on almost every project. But I mostly use the Plates and Gated settings. The short reverbs.
The trick is to set the Pre Delay....setup the reverb and adjust the Pre Delay slider until you find the sweet spot.
 
Another trick I use is to send a vocal to a Delay with only one or two repeats, then I send the Delay signal to the Valhalla. It gives the vocal a ghostly ambient reverb that kind of follows the dry signal and gives it some room.
 
One last thing that very few people mention....EQing the reverb....alot of reverbs tend to add quite a bit of low end, or mids or even highs.... (digital delays are notorious for adding esses and attacks )....anyway removing some frequencies will make a reverb sound even better.
 
My 2 cents.....I love Valhalla Room.....

I usually hi-pass everything up to about 500Hz before it hits the reverb. And also roll off past 10kHz. 
 
If it's a solo part then I may back the hi-pass filter off a bit to around 250-300Hz. 
 
If it's a vocal that I've boosted with EQ, I might also attenuate that frequency in the reverb. 
 
Also worth experimenting with different widths. I like how Valhalla Plate has a width control. For everything else I insert Channel Tools or the Flux Stereo Tool after the reverb. Sometimes instead of using a mono verb I'll use a stereo reverb with a narrow width, say 20%. I often think mono reverbs sound a little one dimensional. 
 
With Channel Tools you can take out some of the mid gain too, which helps maintain the clarity in the center.