From what I have heard thus far, Sam has technically got one of the best "natural" voices to ever make the judges houses on the uk version of the show. She also puts a great deal into her performances, but doesn't overdo it too much. She has musicality and subtlety as well as reasonably good modulation to adorn that big, gorgeous voice of hers,and I like her.
While her voice doesn't have quite the agility of Leona, or the incredibly rich texture of Hannah, it is a clean,reasonably powerful and dynamic, even and clear toned, beautiful instrument, and if I had to make a bet who could nail a Whitney song this season, it would be Sam.
My only criticism is that , because her voice is so good, she kind of coasts on that, and, while it's lovely to watch her joy when she gets into a song, she would do well IMO to try some risks and unique variations of melody/tempo/etc. She has the skills for it, and when she sings these big songs too straight just because it's fun when you have a huge voice and because she "can",it paradoxically can make a standout voice come off a bit karaoke/less serious.Not in the same way as a less gifted singer trying and not measuring up, but it can still be detrimental in the ears and view of some listeners/voters, not to mention those looking for something new in the artists they choose to work with. She is competing against others who could outlast her if she doesn't develop the rest of her stage skills as she has her wonderful vocals.