Story-wise and aesthetic-wise, you missed nothing major in Gen. III and IV. However, they at least deserve a lot of credit for bringing about two definitively worthwhile refinements (abilities via III and the physical/special split via IV) for battling.
Black and White of Gen. V were, in my opinion, fantastic for:
- Being a proper pseudo-reboot unlike Ruby and Sapphire, thanks to its region (Unova) being totally isolated from the first 4 regions
- The majority of its native Pokes were callbacks to Kanto while maintaining their own uniqueness
- Team Plasma, their native villainous team [spoiler=Black and White](especially
, actually having worthwhile depth
Although Gen. VI was, in retrospect, a 7.75/10 at best (and still more enjoyable than Gen. III and IV
), it was nevertheless very important for in changing the landscape by:
- Finally bringing the core series games into 3D
- Introducing the fairy type, which helped nerf the ever-popular dragon, fighting and dark types while also making the situational steel and poison types useful
- Debuting Mega Evolution (although it could've been handled better by buffing jobber Pokemon instead of perennial favorites like Lucario, Tyranitar, etc.)
Most recently, we had Gen. VII
debuting Ultra Space and Ultra Beasts.
Couple that with its region, Alola, following in the footsteps of Unova and Gen. VI's Kalos by being isolated to the point of having trials instead of Gyms, alongside the best villainous team since Team Plasma, and it wound up being a very refreshing change of pace.