Yes, the difference is very minimal (well, okay not that minimal when it comes to the girls and some character recruiting), but if there's one thing about Firestorm, is that I wished they used a Maji de Kansha cover instead of slapping the same cover song from the Blizzard version... (and we get as a result, un-synced video)
The dif is minimal sure, but it makes a lot of dif for people like me that want to follow proper routes and stories. xP
In Firestorm he follows the Natsumi and Gouenji's route.