Like Gatorbait, I too just opened up Mexico.
I can't seem to find a good mix between doing the missions & roaming. I get stuck on one or the other for hours at a time. Last night I played poker for the better part of 2 hours, with Bigdaddy doing much of the decision making...except on Liars Dice. I owned that game myself.
I haven't really ranked up my hunting challenges yet. I think I'm on rank 2 for all. I can tell I'll be playing this for a long time.