I'm watching a Mets Classic on SNY right now. It's Mike Piazza's first game as a Met. Aside from how different the TV broadcast looked and sounded (Howie Rose on TV with Fran Healy), just looking at how Shea looked.
This was 1998, before Shea was overrun with advertising. There was some (like the rotating ad behind the plate, higher up than it was in the final days), but it didn't stand out like it did in the final years. You could really see how blue the ballpark was.
I was there for the game. Field Box (back when it was affordable to sit there and fairly easy to get), right about on 3rd base behind the aisle. I remember sitting there a lot back in the 90s. This was actually the first game I went to early where I could catch Mets batting practice and try to get autographs (before Willie banned player-fan interactions). I was actually at the game before the new Mets star.
Update - there's a lot more advertising than I may make it out to look like there is, but it just didn't stand out like it did in the past few seasons.