I have been learning MVC and eCommerce development on nopCommerce and you know what people ? It's really awesome eCommerce platform. With frequent new releases to make platform much better. They keep on improving performance of the Platform in each new release in every possible way.
I see every version lot more improved in terms of performance and new functionality. The system is a very good solution for small to mid-level businesses, if customized a bit than it can be even used for Large Associates or businesses.
So far where speed is concern, it does not only depends on the application it also depends on the Computer/System/Server configuration as well as internet speed.
i.e. If the server has very low configuration. If website has Images on any page with large size (several MBs). Also, if the server hosted has a slow internet speed or the user who is accessing internet has the slow internet connection. Even size RAM of the web server or SQL server could affect the performance of the IIS/Computer System. :)
Apart from which, I think in your case either the web server or the SQL Server is running on lower configured servers. Kindly note a system with proper configuration makes a lot difference on the performance or the load time of the website. In case if the nopCommerce website is hosted on shared server where the Load Balancing is not configured obviously its gonna take more time to load depending upon the server load.
It also can be possible if you tempered the website to achieve certain functionality regardless analyzing the impacts on performance of the website and impacts on existing functionality.
At last I would suggest whoever is commenting something about the system why not to just load 10,000 products and see the performance, repeat it with 20k, 50k and 100k and see the performance of the system and how much time it takes to load the products on page.
But anyways no Personal offense, despite of all this I strongly recommend users to do some genuine performance testing before posting negative reviews about the nopCommerce platform.
***** (I rate this platform with 5 out of 5 Stars. What do you say guys ?)