I have been keeping count of all the countries I have been in over the years, and this is an anniversary: Malaysia is number 50.
The "executive bus" from Singapore to Kuala Lumpur is spacious, comfortable, and falling apart inside, but I found a seat that worked. The formalities at the border are simple, the bus stops once on the island of Singapore to exit and once on the Malaysian mainland to enter, but the whole thing takes only minutes. We got to the Royale Bintang hotel, with a (partial) view of the landmark Petronas Towers from our room, in the early afternoon and had time to wander.
Like Singapore, Kuala Lumpur is a mixture of modern highrise buildings with thundering traffic, and low-key old districts like Chinatown. This one is fairly small but very lively - four large blocks, bisected by two two pedestrianized streets packed with stalls selling watches, cell phones, bags, clothes, and souvenirs, and there are a number of Chinese hole-in-the-wall restraurants.
We also went to the modern district past Chinatown, but it's basically one big tangle of freeways. Walking is possible but unpleasant. We made it alive to the central train station, and took the elevated monorail train back to Bintang. Looks like futuristic design from the eighties.