To say that gameplay mechanics haven't changed in the last 2 years just means that either you don't play much madden or you aren't very good at it. Defense has changed remarkably between completely different DB AI, Defensive audibles, and the Hit Stick. Well not so much the hit stick, but its fun anyway. Playmaker can also make a huge difference on offense if you get the hang of it. If you're using some crappy PC gamepad it hasn't changed, but if you have a real dual analog pad or a ps2 controller hooked up to the PC you can take advantage of the newer features. I mean a lot of formations and basic option plays weren't even added until 04 and 05.
ESPN 05 is good, its even better in some regards to Madden, I'm not arguing that it hasn't made inroads, but I think overall there isn't much contest. If you're strapped for cash by all means pick up ESPN, but just because madden hasn't gotten a graphical update since 03 doesn't mean it isn't a very different game.