Whoa, from gen1 you jumped to gen4? How did you miss all of this?
Ok so you missed about 100 pokemon in gen2, and another 130+ in gen3. The introduction of pokemon breeding, genders, natures and shinies. You are yet to experience the joys of hatching eggs.
We now have steel and Dark types. Special abilities have been added in gen3 along with natures that benefit one stat and hinder another.
Also, there are now pokemon contests.
You missed Johto and Hoenn, the choice to play as a female character and the battle towers.
And probably much more, lots of adapting for you to do!