Not quite as civilised (or predictable) as what you'd find in most western countries. The roads may not be as nicely designed, many motorists treat traffic rules as suggestions, and many practices are different from what you'd find in North America.

For instance, pedestrians don't get the right of way, you can't make the equivalent of a right turn on red, motorcyclists can be erratic (hit one and you're in big trouble), and parking can be quite random (i.e, almost anywhere you like, even if it blocks an entire lane of a busy road). Plus, Malaysia and Singapore drive on the left

You might survive driving in Kuala Lumpur and Singapore which are more civilised, but I wouldn't try it in Georgetown unless you're used to such driving conditions.

KL and Georgetown are quite easy to navigate around without a car. Uber and Grabcar (the SE Asian competitor) are reliable and quite cheap. Getting between SIN, KUL and PEN is quite easy by train, bus or flight. I wouldn't rent a car from SIN to KUL as cross-border rentals can be quite expensive.