Slowness is resolved with a simple install of the game to your Xbox HD. The interface is cumbersome, yes, but it is no where near as bad as some games I have played.
Unrealistic results... hell, that's just football dude. I mean, think of how many crazy *** games we have seen this season alone! If u actually sit down before u play your career and come up with what type of schemes u wanna run (Vertical Passing, West Coast, Run Heavy, Blitzing, Zone Coverage, etc) then u can tailor your team for your play style and make the best of the game.
Does it have short comings.... no arguements there.. but for all the holes in it there is still a beautiful game that I have enjoyed for the past 4 to 5 months and continue to enjoy.
My advice... Try out a career with the Lions, Dolphins or Falcons and see if u can do better or improve on what they did this season.