For me it's the following
1. Content - huge amount of content which is easily accessible.
2. Interface - Once you get used to it the interface is top notch. I've seen freeview interfaces and the difference is huge. Sky is intuitive, smooth snd glitch free.
3. Boxes - Had it about a year and it's obviously on constantly. Only had to reboot it about 3 or 4 times.
4. Quiet - Had boxes in the past that have had noisy fans.
5. Minibox - having the ability to just plug in a mini-box in any room for an additional one off payment of £99 is good.
Downside - it ain't cheap!!!