Yeah so it's totally different now. Only 6 slots per gym and 1 species per. No more raising gym prestige the fun comes from, as pat said, the cooperative raid battling and trying to take or maintain control of the gym before egg cracks. Unfortunately you missed Lugia the legendary birds and Raikou but Entei is in the Americas now with suicune soon to follow
Also there are EX raids for mewtwo you obtain an EX raid pass by doing raid in Sprint and other sponsored gyms although they are rolling out to non sponsored gyms slowly
Gen 3 is coming out Oct 27 as well