OP, I lived there for 2 years, Lots to do and interesting stuff to see. Number 1 recommendation is to avoid the Touristy / glitz nonsense like Orchard Road Malls and IMO Clarke Quay. As others have said lots of cool stuff to seek out, those who think it’s sterile have just been to the tourist hotspots/obvious stuff
I used to live on Club Street which is very close to China Town, small hotel there is OK with a nice rooftop bar – “the club hotel” I think its called. The street has a lot of older traditional shop houses and many bars and restaurants a lot with a French theme (my favourite place IndoChine closed its branch there). Raffles Place MRT is close-ish by or just take a cab (there is a good taxi booking app you might want to download if you will have mobile data, works well with numbered taxi stands)
Visit the Chinese temple and also the adjacent Hindu one all within a few 100 yards of Club Street and next to China town. The food court / hawker centre there (Maxwell Court?) is a good one too. The Arab Street area with it’s Mosque is quite interesting too. Botanical Gardens if you like that sort of thing (quite sterile IMO but Orchids worth seeing for an hour or so). I haven’t been to the new gardens at Marina bay but they are supposed to be good.
If you wander around Boat Quay / Raffles Quay you can pop into the Asian Civilizations Museum too.
I am not a fan of the Marina Bay Sands but the view at sunset is pretty cool from the rooftop bar
I like an evening dinner by the looking at the skyline by Esplandae (theatre/concert venue), the No Signboard Seafood restaurant is good for your crab (pepper, chilli etc) or other seafood. Its a posh version of the original which you could seek out if you want. You can rent bikes at East coast park but its a bit boring riding up and down a tarmac-ed path (seafood places there too and one or two nice chilled lunch spots, small beach club called Mana Mana which I used to a bit of sailing from the foiling Moths are based there, officially members only but they don’t seem to enforce it). There is a cable tow water ski pond too