i stayed 2 nights at the marina bay sands to finish off our honeymoon after bali. i would recommend trying it once as it really is an experience - for many of the reasons mentioned by QF Lad. we go upgraded too either because of my plat amex or honeymooners. honestly give it a try ONCE!
i wouldnt of stayed anywhere else for our first visit to singapore. however if i ever went back i would go for a more service orientated hotel like the fullerton bay...