Depending on what you are looking for. If you regard ICMS as a regular kindy combined with some Montessori elements, then it is OK. If a parent is looking for a true Montessori school, then it is not. My son was happy there too, but I found their class day unstructured, and teachers didn't supervise activities and the kids during work cycle as much as our old Montessori school. My son, who has always been very focused and even-tempered, began showing signs of bad temper about a month after he started there and it got worse. I had a chance to talk to some parents with kids in the same class eventually, and I found out many wanted to withdraw - only held back because many were waiting for interview with IS. Other than my son, I knew at least 3 other kids in the same class who withdrew immediately after they received IS interview results. However, seems ICMS kids have a good chance in getting interviews with ESF (including my son).
Immediately after I transferred my son back to his old school, I saw his concentration and temper improving and returning to how he was like before (and that was with a new teacher in a different class!). When the teacher showed me pictures of my son at work, I was horrified to find that some Montessori work that he already mastered half a year ago had now all become a mess! That can only mean that at ICMS, they didn't keep him on work that he could do and was doing already or the teacher just didn't supervise him! and I put in a lot of effort when my son started at ICMS. I photocopied our previous school report (6 pages total which detailed EVERY Montessori tool he was working on and at what level), wrote out a list of Chinese characters that he had learned (I taught him myself) and at what level was his phonics. Apparently, the teacher didn't give it much time and then just returned it to me. I even made an appointment to talk to Mr. Chow and the class teacher to give them an overview of my son and tried to gain an understanding of how their class is run.
Overall, just a big disappointment. The kids there are happy. I don't disagree. But if you are looking for true Montessori, then it's not. I took a 90-hour Montessori parenting class, so when I look for a Montessori school, I don't want a hybrid.