NFL2K= A good start, the game was just above average. Insane graphics and great sound but no balance in gameplay. It was impossible to run the ball effectively and there was no bullet pass. Every pass throw was a lob, even if the dude was 10 yards in front of you and standing still. Plus bugs, loads of bugs.
NFL2K1= The best game in the series. Fixed the running game, but made it too easy to run. Completely unrealistic physics and special moves allowed you to shake off a 275 pound defender simply by spinning. Finally added bullet passes. The game still suffered from horrible defensive AI. Out routes, posts and streaks were way too successful. On the defensive side you had the "electric slide" move, which was the only way to keep up with your man on an out route in most cases. Added a franchise mode but man was it horrible. Great online play though. One of the best football games ever made imho, but in no way shape or form was it realistic or anything near Madden.
NFL2K2= Series really started going downhill here. Tried to fix the running by making it nearly impossible to break tackles and also made it too easy to be caught from behind on a breakway run. Passing the ball became a complete pain in the ass because the WR's would never hold on to the ball. If you didn't have a guy named Moss, Rice or Owens on your team, your passing game sucked. Unless of course you utilized one of the many money plays in this game. Franchise mode didn't see a single improvement here and the online play seemed to take a step back.
NFL2K3= Another step down from NFL2k1. None of 2k2's problems were fixed. Running was still a boring 3 yards a carry crap with linebackers chasing down backs in the open field. WR's still dropped everything way too easily. Menus were still unchanged. Bugs? Yes sir. How about the nasty bug that didn't allow a human-controlled player to register a sack? The QB always broke the tackle unless it was the CPU controlling the defender. Laggiest online play I have ever seen. I swear Madden 2003 on 56k was smoother than NFL2k3 on cable. Subtle improvements did not help the still lackluster franchise mode and the menus were exactly the same for the 4th straight year. Another bad effort by Sega.
ESPN NFL Football= Well, atleast they got some presentation changes. Probably a better game overall than NFL2k3 also, but still just a bit worse than 2k2 and not even in the same league as 2k1. Franchise mode seems to have seen the most attention, too bad the menus were impossible to navigate. It was also right up there with 2k1 in terms of realism. In other words there was none.
ESPN NFL2k5= Probably the 2nd best in the series, but far from a great football game. All offense, no defense. This game might have the absolute worst AI I have ever seen in a football title. Plus the franchise mode is useless. The menus are again, a pain in the ass to navigate and the gameplay itself stinks. Pre-determined player progression? That's so 90's. But back to that horrible AI. The only football game I have ever played that was easier to run in is Tecmo Bowl. Just hand the ball off and start tapping that shoulder charge button. An easy 5-6 yards a pop. Throwing the ball isn't much more difficult, seeing how the defenders will run around in circles while you lob the ball up to your player for easy yardage. No one open? Just run for it. In ESPN NFL2k5, there is no such thing as QB Spy. I know in the book is says to hold select while turning the analog sticks counter-clockwise while franticly tapping X while holding L1, then hit the player's icon button. But it doesn't work. So unless you wanna manually take a player and shadow the QB, you're screwed. Oh but wait, doing that means there's no blitz and given time in this game, you can always find someone open. Now lets talk about online leagues. Really, what's the point of offering leagues with no real NFL schedule? Didn't GameDay 2004 offer real NFL schedules? In a 32 team league with 10 games, I still somehow end up playing the same team 3 times? Huh? Worth $20 just as a change of pace to Madden but not worth a penny more.