Plot-wise and character-wise, they are usually a lot better than today's generic manga.

Alice came to a fork in the road.
"Which road do I take?" she asked.
"Where do you want to go?" responded the Cheshire cat.
"I don't know," Alice answered.
"Then," said the cat, "it doesn't matter."
~Lewis Carroll, Alice in Wonderland

As long as the art isn't too bad, and the plot is good, I will read it. The quality matters more to me than the date.

Nulla in mundo pax sincera
"Always go too far, because that's where you'll find the truth." - Albert Camus

older manga that survive today clearly has distinguishing qualities that we can call awesome. added to equation that older things most times triumphs over the new thing (because you are used to it), all this talk will turn into whining in theme of "good old times."

i, on the other hand, believe each eras has good cultures products and bad ones. and since i live at present time, i find good products of this eras is more accessible than the old. so here i set aside my nostalgic tendency and state "today's manga is more enjoyable. you can find more of it if you want."

grammar mistake is intentional, grammar nazis need their entertainment.