I have Fallout 2, I'd like to try the orginal. Is it worth it?

yes

Absolutely. Many of the references in Fallout 2 will be explained. In a lot of ways Fallout 1 is better. It fits the setting and atmosphere more but, as it should be, the developers tweaked the engine after the first game so when it comes the NPC control, you have even less then in Fallout 2.

Is it as long and open-ended as Fallout 2?

F1 is half of F2: it is shorter, has less items, very few upgradeable ones, 80% of containers throughout the game is empty (in F2 it is about 40%), fewer joining NPCs, fewer quests...
It is not so bad, although. I played the sequel first, too, and I was a bit disappointed after playing original. I am glad I've played both games, but I am a bit disappointed.

You should play F1 if getting it is not a problem and you liked F2. But it is not worth much trouble. Consider playing FT:BOS.

I personally prefer fallout 1, I don't know why but I always get bored half-way through fallout 2 a problem I've never had with the first game.

p.s I agree with the new JR Jansen playing Fallout 1 will make you apprieciate the second one more as a lot of the fallout 2 easter eggs will be understood after playing the first game.

What particular easter eggs? Except Mil. Base.

Even if it is true that Fallout 1 have less NPC, items and places to explore, it has one of the most original plot set in the post nuclear war era. Fallout 1 is definately worth a try if you really want to immerse yourself in the story and not too fussy of these shortcomings. BTW, after playing Fallout 1&2, I still think Fallout 1 is a much better game.

Hello,
yes, indeed. F1 does better "fit the mood". It lacks some of the refinement of F2, yet it is close in quality. Fun, fun, fun.....

- Twilight

Let's see.
Shady sands aka NCR.
Vault 15's raiders, you see their predecessors so to speak.
The entire 'how mutants came to be' story, remember Marcus' dialogues.
Vault 13.
Tandi.
Why VC has so many waterchips.
The ghouls in Broken hills talking about Necropolis.
The 'Cafe of broken dreams' random encounter.
etc, etc.......