I liked the new Pokemon introduced in 4th gen. Seriously, aside from the real obvious reason; the further evolution and pre-evolution of summa da older Pokemon. Leafeon is automatic win. LOL
They did have a couple of original gen introduced Pokemon I actually like. Including the Starly-line and Shinx-line, I also was quite fond of the Finneon-line and the Stunky-line.
Basically, after 2nd gen 4th is my all-time favorite.