The peaking of 90210 started in the Summer of 1991 when the 2nd season aired, but by season 4 its almost sky high. It was a different setting which helped, the college setting as opposed to the high school setting, meeting new people and the gang was essentially growing apart, particularly Brenda who was ready to conquer the world far away from the zip code. It also put character relationships back to basics, almost a reversal of season 1, Brenda and Dylan are friends not lovers and to be honest in retrospect, I'm glad that the triangle happened even though I still hate Kelly for it, but aside from that it gave the shows first supercouple new, uncharted ground, Dylan himself was ready to move on from the zip code and this kinda puts a barrier between Brenda & Dylan and the rest of the gang. And as for the rest of the gang Andrea also undergoes a number of changes, the perpetual virgin, blooms as she takes not one but two lovers, one of whom impregnates her and later marries her This also removes Andrea from the group somewhat. Seasons 2 and 3 we saw the whole buddy buddy gang stuff with the big 8, where as season 4 they're all finding and forging different paths away from the comfort zone, Brenda with her acting, Brandon with his politics, Andrea with being a mother and a student and Dylan with his so called newfound family Season 4 was the last good season of 90210 and possibly the shows peak I would say, the following six years weren't so good, I would've stopped 90210 at season 7, as seasons 8, 9 & 10 really didn't need to happen. I've always said that the Kelly-Centric attitude of the show was what killed it, she was overused and every plot somehow involved her, even if it was something unrelated to her own storyline, she was still just there and the character became worst Tha what she was in the early years when she was a sweet natured girl, who could be bitchy but had had heart in the right place, season 2 Kelly would hate season 6 Kelly for being a judgmental jerk toward Valerie. But yes i would say that season 4 of 90210 was the shows big peak wouldn't you say?