1 is definitely worth play, and it's self contained so you don't need to play later installments if you don't wanna.
This is gonna be an unpopular opinion, but I liked 2 for what it tried to do. I liked that it was a low key story about a guy just trying to make his way and not a story about saving the world. I like the character writing to an extent, though I'll be eternally dissapointed about how Anders turned out. The concept was actually pretty good but the execution was sorely lacking. But even for everything I liked about it, it was a rushed mess. The combat was boring and tedious and there were like 6 dungeons that were reused infinitely for the entire game.
If you are willing put up with that, I think it has the best character writing in the series Anders aside.
3 was just kinda generic. The combat was better than 2 but still not great. The maps had a lot of variety which was a big improvement, but sadly it felt like a single player mmo, running around doing generally the same things on each map, with all the story content off in instanced areas rarely connected to the big sprawling maps they made. Probably one of the biggest flaws the game had. The story was just ok, nothing special. It did feel more high fantasy compared to Origin and 2's lower fantasy tones. It had some of my favorite companions but also some of my least favorite companions, with the rest being forgettable IMO.
It'll probably be mandatory playing for DA4 though considering endgame revelations.