YouTube-creator Black Pot released a video with the comparison of GTA: San Andreas — The Definitive Edition and SA_Direct 3.0 mod for the original game. It is pretty stunning video that shows that the modders are the tip of the spear and Grove Street Games couldn't catch up. There are no volumetric clouds in the remaster, and the mod amps them up to nowadays games standards. The feeling of the speed and the blur are also implemented better in the mod. However the draw distance is lacking in SA_Direct 3.0 since it uses the original GTA: San Andreas engine. When it rains in GTA: San Andreas — The Definitive Edition there are simply no reflections on roads. The mod however provides almost AAA-quality reflections. Overall the weather looks way better in SA_Direct 3.0.
The author states that the mod is definitely a winner here. He thinks SA_Direct 3.0 just needs more polish and optimization. You can download the mod here, on LibertyCity.