Let's get the bad out of the way. It took Glasgow Rangers to toughen him up after Jeremies slapped him up and down the Republic of France in 1998. He was farm-raised, free-range garbage against Ghana. His professional career was plauged with injuries literally from start to finish - he missed the 1994 World Cup, and he retires on the MLS injured list. Nothing became his MLS career like the leaving of it - he and Tab Ramos could feed Africa for a year on the money they stole from the MLS New Jersey franchise.
Now, let's think back on the 2002 World Cup. Wow, was he ever great. Wasn't just me that thinks so either, of course - FIFA put him on their First Team for the tournament. (It wasn't a First XI, so we'll never really know whether he would have made the theoretical starting lineup....but we know he would have, he was better than Rivaldo any day of the week.)
One of the few Baby Jesuses to actually live up to some of the hype, although not the infamous prediction Time magazine made that he would be one of the most influential people of the new millennium, or whatever the hell they said. Out of American field players, so far only John Harkes before him and Brian McBride after him have had the kind of respectable European club career that Reyna did.
And, of course, there are the 112 caps. For most of those 112 games, Reyna was the team's unquestioned leader, the crucial figure in a period when the team reached its peak, so far. In the long run, Reyna will be seen in the long term as a transitional figure from the USSF "club" team of the early 90's to continental colossus and international acceptability. Better players and better teams will have to arrive for the US to make a further transition into international greatness...if that day ever truly comes. For now, the 2002 World Cup team is the greatest US men's national team to take the field, and Reyna was their captain. That's a fine legacy.