what i know from experience of a close buddy who is studying chemical engineering at NUS, he had a mediocre result in O-Alevels:-
yes its very competitive but it is worth a try for those who got straight A's in Alevels and equalant degrees.. A healthy co-curricular background may give you an advantage. Luck is a very important factor. its a lovely place to study. living expenses are generally high. there are numerous scholarships and student loans, bursaries and several programs to cover major part of your tuition fees. the study is very hard and will beat the sh*t out of you.