We have been to Twin Towers - KL Tower - Hop on Hop off bus. Just want to make sure we have it covered.
I would not miss Chinatown and a stroll through Little India. Also, I'd see the Thean Hou Temple while I was there. The Masjid Negara and the Islamic Arts Museum are both nice. I always like to go to Pasar Sini for a little handicraft shopping. And the Lot 10 food court is great if you want hygienic but authentic street-food, but I also really like the Jalan Alor Hawker Centre -- maybe not as clean, but great.
The link below is to an article, KL in 24 Hours. I think it has the not-to-be-missed things. http://www.southeastasiatraveladvice.com/2011/06/kuala-lumpur-in-24-hours.html over 6 years ago
Here is a consolidated list of things to check out in KL and the surrounding region. Try the Chiling waterfalls and Batu Caves - great little day excursions from downtown KL!
http://chasingplaces.com/4-must-see-tourist-attractions-in-peninsular-malaysia/ about 5 years ago