Imo (and most other fan’s opinions) you should absolutely start with the OG, if nothing else than to see how gaming has evolved and such.

If you’re feeling it, I’d recommend just jumping into BM. With the original being so fresh in your mind, you’ll really appreciate the work these people put into their remake. It’s so full of love for everything in the original (and a bit of HL2) that it still kinda blows me away with all the little details and such. The scientists and other NPCs all look distinct now and have different personalities and voices, and before shit hits the fan you’ll hear plenty of little banter and idk chat between your coworkers as you make your way to the rest chamber.

There’s also, as a mod for Black Mesa, another team remaking Blue Shift in the new engine and all. They’re not done with the game yet, but what they have is about 3-4 hours worth of story finished (the first 5 or 6 levels I believe), and it’s actually expanded on even more than in Black Mesa or the original Blue Shift. There are more named characters, extra parts added to missions, and it feels like the same care went into remaking Blue Shift as went into making Black Mesa.

There’s also a fun part at the beginning that has an overlap with Black Mesa where you, as Barney, see Gordon go by in the tram, and I think he flips you off in like a teasing playful way.