Believe it or not - I'm also a fan of the Disgaea series 
MY recommendation & suggestion (if you're only interested in the PS3 games), would be:
1st play Disgaea D2: A Brighter Darkness (because, it's the same characters from the 1st game on the PS2 (arguably the best game in the series) but - more importantly for newcomers to the series...it's BY FAR the most polished & accessible game in the series,
2nd play Disgaea 4 (because I like it better than D3), and
3rd play Disgaea 3 because, while known as the weakest & least popular game in the series...IMO, it's not a "bad" game and it's still worth playing (*Last*). 
Really, you are too???
xD
I haven't played D2, but I wouldn't doubt that that'd be a good place to start.
Personally, I actually thought 3 had the most attractive story. While the whole 'High School' thing has been overdone by now, I loved the sort of backwards-logic surrounding the idea of having to become a good student to be the ultimate bad student. That just really caught my attention for some reason. XD
I'm just not a big fan of 4's story so far. It's not bad, but it doesn't have that same sort of 'mental stimulation' that 3's idea caused me to have.
But again, I've never gotten more than 20 hours into any given entry, so yeah. xD
For the OP, just don't get discouraged, as there really is a bit of a learning curve to the game (heck, even I still get a bit confused by geo-blocks sometimes). But I'd say it's worth it, as I think Disgaea just serves as a really good model of how to make a solid game. The humor isn't always up my alley, but I like to admire it.
Oh, and all the games are available on either the PSP or Vita, so if you have one (and prefer handhelds) that's another viable option. They also generally have a bit of extra content as well.
