As a 'moderate' fan of tactical jrpgs the Disgaea series has always both intrigued and scared me at the same time. Intrigued because of the grind, as you can famously get up to level 9999 (many would say it's a bad thing but I'm weird so I like it), and scared because of how complicated it looked as an outsider to the series. So, after years of procrastination, last week I finally decided to play it.
I decided to start with Disgaea 1 as it seemed to be the most simple (after all, it's the first game in the series) and oh boy am I loving it! It's a cute, funny story with no pretenses and some pretty memorable characters. It's the first game in a long time that genuinely made me chuckle at times. The grind is there, and I like it (I'm one of those people that always needs something to do, even while I'm listening to a podcast or watching videos) but leveling up and "transmigrating" (aka starting over from level 1 but with boosted stats and possibly a new class) is pretty satisfying. I haven't finished the game yet but I'm near the end of the main story. Unless things suddenly go south I think I've found a new series of games that will drain my time for the rest of my life, especially since I expect the sequels to fix some of the biggest QoL concerns (the menus are a bit clunky at times).
So yeah, that has been my experience with Disgaea 1 so far. I'd recommend it, especially if you like the grind.
I would say it depends on which is more important to you story or gameplay. They definitely made 6 easier which I personally liked, I was able to do everything except defeat Baal on the highest difficulty (I didn't want to grind another 20-30 hrs just for that).