The Insight has a stiff ride. It makes it seem more sporty, but being more sporty than a Prius is not saying much. If I want sporty, I will get a Boxster or S2000.
I think the workmanship is the usual Honda top notch for the money, but the materials feel cheap. Both the Prius and Insight could use simple upgrades in their dashes.
The engine noise is annoying in the Insight. Both the Prius and Insight have engine noise, so if you dead quite inside, you will need to get a Lexus.
This is a glaring issue with the Insight. Leg room is for children and my head hits the roof and a little bit of the rear hatch. There is a warning sticker about making sure go watch the heads of your rear seat passengers when closing the hatch.
There are more safety and luxury options on the Prius. You can tell Honda think the Insight will only be for econo car buyers, while the Prius is trying to appeal to mainstream buyers.
