My 2 daughters are currently enrolled @ ISS. I only looked at 3 schools and it was the only one that could accomodate both at the same time. They only started a few weeks ago (2nd week of November).
I have a 4yr old and 8yr old. The 4yr is in K1 and the 8yr old is in K2. Since your child is fairly young, I don't think it will make much of a difference in terms of programs, at least not at this age. My 8yr old was in the 3rd grade in the USA and they put here in the 2nd grade because of her age. Again, my wife and I think that at this age (5 yr), it's more the socialization than the actual course content that is important. Most of them will be the same in terms of course content: art, a little bit of basic math, spelling, basic words, shapes etc.
Am I happy with ISS? Can't really say at this point, at least with regards to my 8 yr old. I'm beginning to realize that even though it's IB accredited, IB in and of itself cannot be evaluated by a mere semester. You have to look at it holistically as the program is designed in this manner (multiple years). Coming from the USA, I tend to look at results on a class per class basis. I'm not happy that my 8yr old daughter isn't challenged in her current class. As an example, she can do 3 digit multiplication and the class is still doing single digit addition. They're supposed to provide some additional callenging homework, though. It almost seems like that within the context of an IB program, it's not very flexible. In contrast, our 4 year old is doing well and no complaints. Again, we consider the socialization aspect as the most important. For your 5 year old and the 2 year duration of your husband's work, he/she would be fine @ ISS - IMHO.
With regards to the school itself, the administration is pretty helpful and responsive. For both grades there's 2 teachers, a main one and an assistant. The facilities are somewhat aged and they don't have a pool, nor a gym, at least none that I could remember. They do have some agreements with another facility for pool useage. Teaching staff appear to be caring and they limit class size to ~20 per class. I looked at the security and it was fairly safe. They keep the kids in the higher grades (Grade 5 and above???) separate. They try not to comingle the 2 populations. Teachers haven't had very high turnover. From what I remember asking, their teachers have been there teaching for at least 2 years on average. It is an IB program. Something to consider for the long term.
You could always use ISS as a starting point until you get here and do a better search and then subsequently transfer to another school that you feel comfortable with. One item to note is that the Singapore American School
(SAS) has referred students they could not admit due to space limitations to ISS.