From what I've played, they're grind heavy. Seeing characters over Lv 1000, and have like 6-10 digit stat points is pretty overwhelming and insane. It's not that bad right now in D4APR. Do the code that lets you unlock everything in the beginning, and it's gonna unlock a guy that lets you add people online to help you win a round. They're over Lv 100, so just get monsters who are Lv500+, fuse them, and Magichange them to the character you want to upgrade. By the end of the just the first round (consisting of 5 matches), you can go from Lv20 -> Lv 100+.
The main story isn't that gind heavy, but it's easy to stick get yourself stuck in a position where you need to grind hevily if you are not careful.
(this part directed at Charizard Champion)
What really helped me was looking up Disgaea on Before I Play. It had some good advice. Mainly that you shouldn't try and have a full party since it splits experience more than you will probably need and to ignore reincarnation at first since you don't need it to beat the game.
The big thing with Disgaea is that it is a really open experience, so it's easy to get caught up in making your little people and awesome and you forget that your goal is to beat the game, so it takes a little bit of tempering to deal with that.
If you just want to play through and enjoy the main quest, I recommend starting off really simple with a small well equipped party and only adding on or upgrading characters when you really need to. And realize that some of the parts of the game really do need some strategy. (so look it up online if you are stuck)
I am trying to figure out a good way to enjoy as much of the games content in a single playthrough, ithout getting any long grindy parts, but I am a littloe stumped in figuring out the best way to do that.
And the bolded parrt above. I didn't know Disgaea had cheat codes. It's been forever since I have heard of any game with cheat codes. I miss them.