My thought at first was the 2 games were very similar to their predecessors, however there are quite a few changes which take a while to notice at first.
Firstly, FIFA 11 has introduced a more thorough way to organise your defense, a lot better than you could in FIFA 10 anyway.
PES 2011 also has a much better penalty taking system, as the one in PES 2010 was quite..shit. This made it much better to take spot kicks, and could be groundbreaking for online game modes when the perfection of a penalty matters so much to the player.
Overall, however, I was unimpressed with the content of the demo's. After almost 2GB each, I expected something more than 2 teams per game, Barcelona & Bayern Munich on PES and Chelsea and Barcelona on FIFA.
However, both games themselves were impressive and I can see the competition between the two becoming even stiffer as both companies try to outdo the other.
Here are Lionel Messi and David Villa's first impressions of FIFA 11