However, the 29-year-old has performed on a consistent basis having netted 20 or more times in the last three campaigns in the top flight, and has a tally of 128 since his switch to City from Atletico Madrid in 2011.
While discussing the league's top strikers during Sky Sports' Monday Night Football, Henry said: "The only one who is world class, or has been world class, is Aguero because of the longevity of what he has done in this league, year in and year out.
"He won the league here and he has been doing it the longest. You have to give him a bit of credit. I think sometimes we bypass Aguero like he didn't happen."
The Argentine has scored six goals and produced three assists in six league outings so far this season.