Hi zapteo and secretsquirrel,
Yes, I taught at SIS for three years and teach quite a few kids who are students there now so I know the system pretty well, but like any school it is constantly changing.
There are nearly no caucasians at SIS and the majority of students are from mainland China, Singapore, Hong Kong, or Malaysia. In that sense it is not as international as many other schools. The teaching philosophy, as I mentioned before, is exam oriented and there is more focus on exams and results than you would get at ESF.
It's hard to define "fun". They children know they have a lot of work and that the expectations are high. Those that move to ESF, recognise that it is "easier" there and a more relaxed system.
Most expats have not heard of SIS and most will go to a school that follows a western syllabus (ESF, HKIS, AIS, CIS). If you are Singaporean or want your child to get a very good grounding in mandarin then SIS is great. Also for local children who struggle to get into one of the other international schools, it can be a good stepping stone. It also depends on your child and how they learn best, some thrive in this environment and I have seen kids do really well.
If you are Singaporean your child will not fail the interview, even if shy. The success rate at interview depends on the number of spaces they have for that year. Most schools will call your child for interview. Teachers are experienced at dealing with shy kids and it is very normal, especially with the younger kids.
Try not to worry or stress as your child will pick up on this. If possible, talk to the school and find out what the interview involves and prepare your child.
Good luck and all the best,
Sunrays