Mexico can be an incredible experience, provided you stay smart and the water is not too high. I have done the first descents of the Rio Moctezuma, Rio Mesquital, and the Rio Urique. All were experiences of a lifetime. Each were at low to medium water levels and it was obvious that we were glad there wasn't more. Most Mexico rivers seem to be Black Canyon style. You are trapped within deep gorges and canyons. Scouting and portages can sometimes be difficult, if not impossible (I do not recommend the Moctezuma for this reason, blind forced class VI). The season is generally best in the January to early April time frame. Beyond that the rainy season begins and the expeditions could be very wicked within the walls of these places that are generaly filled with car and house size boulders. Always be very careful. Steve Daniels had to be resucitated and legs amputated on the first attempt of the Mesquital on day one and ended the expedition. Sieves between the boulder choked walls can be very dangerous. Also, banditos were a danger for us back in the '80s and '90. I don't know what it is like today. I know there are easier rivers, like the Aqua Azula, down there. So it will, of course, depend on were you go. I do recommend Mexico to be boating while it is snowing in Colorado. Expedition boating is always an amazing experience. Just be really a smart, strong, and with a group of qualified boaters. The above mentioned guide Mexico River guide book is very old and not that great, but a good place to start. Also, a word of caution is that Mexico maps SUCK. Be prepared for potentialy longer and steaper descents than you may think. Have fun though. Allow extra days in your schedule. Anything can and probably will happen. I really want to do another one myself and wonder if any first descents are left down there. Cheers!