What are the philosphical differences between Gaudiya Sampradaya and Nimbarka Sampradaya? I know they both worship Radha-Krishna (unlike Pushtimarg where they worship Krishna as ShriNathji). What are the characteristics of these sampradayas which set them apart from each other?
The Gaudiya Sampradaya worships Sri Radha Govinda in parakiya (paramour) mood, in manjari bhava. The Nimbarka sampradaya worships Radha Krsna also but in swakiya (wedded) mood, in sakhi bhava. They have sambhoga rasa (union) and Sri Caitanya Mahaprabhu has vipralamba rasa (separation). In separation mood the gopis are remembering Krsna and having visions of Krsna and in these they experience the appearance of Krsna. So this is Vipralamba sadhana in line with the Srimad Bhagavatam.
Refer this link: http://www.bvmlu.org/contemporary/witdbngs.htm#:~:text=The%20Gaudiya%20Sampradaya%20worships%20Sri,)%20mood%2C%20in%20sakhi%20bhava.&text=Other%20Vaisnavas%20are%20also%20worshiping,following%20Radhika%27s%20great%20separation%20mood