Viewers excited at first? That's right! (4)
I believe the answer is:
eyes
'viewers' is the definition.
(I've seen this in another clue)
'excited at first? that's right' is the wordplay.
'at first?' indicates taking the first letters (I've seen 'at first' mean this).
'that's right' becomes 'yes' (right can mean yes or okay).
The initial letter of 'excited' is 'e'.
'e'+'yes'='EYES'
(Other definitions for eyes that I've seen before include "Ophthalmologist's speciality" , "Storm centres" , "Looks at carefully" , "Parts of needles" , "Globular organs" .)