Legroom in the rear is tight. You would want to put smaller passengers in the rear if you're taking four people along. I was able to put my overloaded briefcase between the front and back seat on the floor, but it isn't a wide area back there. Front seats are individual buckets with a decent amount of side support, about the same as the old VW Beetle. For the rear seat to accommodate two passengers, the front seats should be on the front stops.
Acceleration is decent.
Entry onto Interstates requires some planning. In order to get up to the ambient speed of the traffic you need plenty of merge and acceleration room. You can get all of the performance out of the Kia you need to drive safely on any road. Kia used an intelligent approach when it designed the Sephia. It didn't try to break new ground.