I did Singapore to Malaysia and Thailand on Royal 4 years ago and it was amazing. The ports were Singapore to Port Klang (and then a bus ride to Kuala Lumpur), Penang Malaysia, and Phuket Thailand... and then we spent time in Singapore after the cruise as well as Southern Malaysia before flying to Bangkok for a couple days. Klang didn't seem to have much at it and the bus into Kuala Lumpur takes a very long time limiting your actual time there (but we managed to get a lot in!) Penang was stunning. We did an Excursion that involved taking a mountain tram high up into the hills as well as a fantastic temple tour. Phuket was very much Cozumel or Nassau vibes, we did a highlights tour that got modified and we missed the highlight we actually booked for.....but what we did/saw was pretty cool and we got some (short) freetime at the end to explore a giant mall and the tourist Market stalls near the tenders.