So I know only this one song by chicago and it's really really good. I LOVE the wall of horns playing with themselves and the heavy guitar riffs.

However, I'm not going to listen to all 75 of their albums to find the few gems. So could you kindly point out the really really good songs so I don't have to wade through hours of generic dad rock (sorry dads)

hey that's a really good one. I'll check out their very first albums, thanks!

More suggestions are welcome!
Terry Kath was Chicago's guitarist and one of the vocalists from the beginning until 1978, when he died from an accidental gunshot to the head. I have always been a fan of Chicago, especially the earlier work. Tons of individual talent that blended well into a great band with a lot of diversity in their songs.

Songs to check out:

Dialogue (Part I & II) Album version (Listen to him wail away on lead during Part II)

Feeling Stronger Everyday (Great rhythm...and bass, too)

South California Purples (Guitar based song)

Listen (Pretty long sustained note during the intro)
All the early Chicago albums are great. Google is your friend. Fall in love with the band. Not one song.