The teachers, without a doubt.
DS's Y3 teacher is absolutely superb. She's been teaching for 30 years, and has seen pretty much everything that small boys can throw at her, including my DS's mega-high-functioning Aspergers. She is slightly scary (on the surface), but is at the same time kind, fair, and funny. DS has been truly lucky to have had her this year. Even more fortunately for him, he had a similar teacher last year. He's also being 'mentored' by an older male teacher, who is fantastic.
I can't speak highly enough of them. They are inspirational.
More prosaically, I like the fact that I have to do stuff all with the children outside school, because school covers the lot: piano, additional instruments, voice, swimming, football, cricket, horse riding, ballet (if you want it), etc, etc, etc. are all available during school hours.
At both my DC's schools, the children all know one another and all the staff know all the children. My Y1 DD goes to a 3-18 school, and the teachers and office staff in the 11+ bit know who she is, as do the big girls. I do like that very much.
I am also impressed with how DS's school (and his school before this one) has handled his extreme cleverness.