For a large company, the interview style is actually quite informal.Technical questions are unlikely. Having said that, my interview was five years ago so this could have changed. They are more likely to make sure that your eyes are open to the less positive aspects of life in Singapore. These include the price of cars, property etc.
If all goes well, sim ride will follow. Usually a B777. Nothing to prepare as they are looking at basic handling and CRM skills. You are not expected to know about the aircraft systems but it obviously helps if you have Boeing experience.
Tyr not to take too much notice of the negative remarks within these forums. SIA is not a bad company to work for and like most things, what you get out of it depends on what you are prepared to put in.
Hope this helps and best of luck.