One friend has come in and is quite excited (8)
I believe the answer is:
animated
'quite excited' is the definition.
'animated' can be an answer for 'excited' (thesaurus). I'm unsure of the 'quite' bit.
'one friend has come in and' is the wordplay.
'one' becomes 'I' (Roman numeral).
'friend has' becomes 'mate' (I can't justify this - if you can you should give a lot more credence to this answer).
'come in' is an insertion indicator.
'i'+'mate'='imate'
'imate' placed inside 'and' is 'ANIMATED'.
'is' is the link.
Can you help me to learn more?
(Other definitions for animated that I've seen before include "put in spirit" , "full of beans" , "Fired" , "in cartoon form" , "Full of excitement, lively" .)