Time travelling and religious services

I attended the first day of RH at a reform congregation, the second at a conservadox. Two VERY different services, but both followed the same structure, prayer order, etc. Barchu, shema, amidah. Shacharit, Torah service, Musaf. It made me wonder… How far back in time would I have to go before a Jewish service would be unrecognizable to a 21st century Jew? (Excluding wacky offshoots like jvp, of course)