HG/SS are the gold standard for me.
Took the best games in the series and gave them updated graphics and music. You can’t beat that imo.
Think that's a bit of an understatement actually. All the remakes do that. HG/SS succeeds by being an actual improvement over its predecessor while retaining the heart and spirit of the games and adding in new things to do that are actually fun to play. And more than that, functionally it's better than most of the non-remake games in the series. It's aesthetically pleasing, feels modern while staying tight and focused in the gameplay and progression. I mean I'd so much rather play HG/SS than D/P/P. If I'm being honest I'd rather play them over any other version in the series.
FR/LG was basically
just a GBA coat of paint and very minor musical upgrade with nothing more it expanded on than moves from Gen 2 and 3, a few other minor mechanics from past games and some forgettable and unrewarding islands you can visit with a handful of non-Kanto pokemon to catch. People complain about the laziness of Sw/Sh but I think FR/LG is the laziest entry in the series by far. I mean you can't remake the most basic game in the series and only add a crap battle tower, the sevii islands, and updated moves and really justify the effort.
OR/AS was an example of taking changes and improvements a few steps too far. I felt like they were decently faithful to the originals but somehow ended up losing a lot of R/S/E's charm along the way. It was kind of amusing to me but also a bit of a bummer to compare my playtimes on my 3ds where I sank something like 470 hours into Y version, 250 into Moon, and only 33 into Alpha Sapphire. Maybe part of it was Pokemon burnout but as I made my way through the game I just kinda stopped wanting to finish it.
Like you said HG/SS are the gold standard. I really hope they try to play to its strengths in the Gen 4 remake. But really D/P/P was the most ehhh, not great, not bad, I guess good entry in the series so they'll have to try to mimic HG/SS's strengths while making D/P/P more interesting and memorable. Feels like a tall order.