Heck, I'm glad someone finally asked about the game.
It is a challenging game at times, especially in the beginning in NFL Challenge mode. You start out with a sucky team, but get development points to build up stats. You'll eventually get better, and it's rewarding to see your offensive/defensive stats match up to the teams after awhile.
OTOH, I HATE the computer's home cookin' on Challenge, but it's there for a reason.
I still have yet to play the Legends, but I heard their stats are freakish. Once you beat them, however, you get to pick a legend for free (no challenge tokens needed).
Maybe you should rent before you buy -- just a suggestion.
I've been thinking about getting it because it seems like the kind of mindless, no penalties, no finesse, kick ass football game that's perfect for when all the guys are over. That's why I loved Tecmo Super Bowl so much: any geek could pick it up and whoop you in about five minutes.
"Also, don't incur the wrath of P.U. It can only lead to trouble." - Torchslasher
I was thinking along the same lines as what Overmind had suggested, once I realized that yeah, it'd never work with American-oriented mass combats due to the firearms factor... Medieval Europe in general, however, would work quite well.