I like Exp. and really try to use it to my advantage. But I have no idea how the new system works.
I've looked and looked at it. And I can't figure it out.
BUT I do know this.... 30/60/90 are when you gain "Ranks"
And upon gaining a rank you don't just get +1 to your HP/DMG like in the past you get a much larger boost like +3 (However I have yet to see it go on Damage first, so I think it always goes HP now)
But from there it get's kind of strange. You don't gain another "Rank" at the next "Milestone" instead it happens faster the second time, (like 70 exp for heavy and 20 for infantry)
But near the end. I think it was taking more than 90 exp for them to advance.
But after the first one it does seem to go back to Randoms. So now you can get HP then another HP. I don't know if you can get 3 in a row though.
That's about it.