When I finished Pokemon D/P, I got bored of Pokemon. I had been playing the series since its beginnings with Red, but D/P's lack of innovation (aside from the much much needed SpAtk and Atk switch) made me abandon the series until some time in late 2013. After browsing through some videos about Black/White and in anticipation for X/Y, I picked up Pokemon White to catch up on the series and I completely regret missing out on Gen 5 when it came out.
Gen 5 is easily my favorite because they finally broke the formula.
Black/White was really story driven, characters had more to them than they did in previous installments, gym leaders took part in the ongoing events caused by Team Plasma instead of sitting in their gyms like statues, they gave meaning to the journey of "completing the pokedex" as a way of learning more about yourself and taking the first step into adulthood, the final boss of Black/White isn't the champion, and Ghetsis is by far the best villian in the series.
I also found the AI in gen 5 more challenging than other gens (but it could've just been my team), while people complained gen 5 had some of the most bland pokemon it definitely gave us some of the coolest (Serperior and Hydreigon <3) and most OU pokemon, and holy shit is Shota Kageyama a godlike composer.
Black/White 2 serving as sequels instead of the 2-in-1 game of Black/White is the best decision Gamefreak has ever made. Seeing already lovable characters return and matured really hits in me in muh feels. The Unova region grew and made to look even more beautiful than before, and the PWT that lets you battle gym leaders and champions from all the known regions with modernized themes was the best feature of Black/White 2.