The best thing about vissim is that it's free to use. It's easy to use too. You can easily create your own models using the provided templates or you can download other 3D models from their website. I have used this product for my final year project. I didn't find any major problem with its functionality except that it doesn't support very large files. If you are looking to make an interactive simulator then this software is suitable for you. We developed a model of a hospital emergency department to simulate the flow of patients in our hospital.