TPM:
Tatooine in general. It dripped in ANH nostalgia while giving us more of the landscape and culture.
Qui-Gon was admirable.
The lightsaber duel; pure bliss and action abandon.
AOTC:
Tatooine, again, however brief (my favorite Star Wars planet).
Naboo.
Portman was especially attractive.
ROTS:
The pervading mood and atmosphere.
Ewan McGregor, most notably at the lava bank, pouring his emotions out.