OpenERP, Odoo is a powerful engine and has many custom designed apps. One can build powerful ERP based on that.Whereas, ERPNext has a very user friendly UI and easy to understand processes and most processes are part of package, while odoo has them as apps. ERPNext is very useful for Small, medium enterprises and start-ups.
We tried working on odoo, but found it difficult without external help. Moreover it is designed for European business method and is incompatible for Indian business processes. We couldn’t do a plug and play.
But with ERPnext, I am practically able to do a plug and play. Some customisation was needed, but it was easily manageable without programming.