Considering the recent developments, I seriously question the efficacy of the deal. Nonetheless, it will remain one of the biggest diplomatic successes in Obama's legacy.
I do think, the nuclear accord has had a significant impact on Iranian domestic and foreign policy. The deal has widened the gap between the moderate clerics and the hardliners who have warned of "nuclear sedition", aimed at derailing the Islamic Republic from its "revolutionary path". The deal has also resulted in a more aggressive Iranian posture to exert itself in the region, leading to Saudi fears. It has had a significant impact on the oil market. The nuclear deal in itself just deals with Iran's nuclear ambitions (questionable) but it has ushered Iran into a new era of relations with the world and improve its political and economic situation at home.