I think that Graphic-wise, HGSS is better than Platinum. Platinum had a huge variety of trees and mountains, but let's not forget for instance HGSS' splendid work on caves, and water, I can go on and on and on.
I personally think HGSS is better.
But we all have different opinions, right? :P
But to answer the question properly, no, I don't think the games were a let down.