I find it a very good improvement on previous EA football games, although I was already quite happy with FIFA 2005. I never got to purchase the regular (non World Cup) FIFA 2006, although I played it a couple of times and see why many find it a disappointment and a step backwards from previous editions.
In WC06, the nicest innovation is Global Challenge, where you can pick among 30 or so scenarios of historical games, and see if you can match or improve on the performance of the team you are handling. In a few of these, you are given the game at minute 0 and challenged to meet a particular score; in others, you get the game pretty late, or at a critical penalty or free kick.
Also, unlike other WC games, this one lets you take a team from qualifiers, not only at the WC finals, and you have almost 100 national sides to choose. Additionally, you get many more players per team than previous editions (in a couple of countries, your roster is 40 names long).
It takes a while to get used to the new way of handling corners, penalties and, especially, free kicks; once you do, you find that the change has been for the better. It takes a while, also, to get used to a few new controls, and that the lag between pressing a shot and having the player actually shoot has been extended.
The unlockable features are neat, especially invisible walls (of course, very unrealistic, but fun) and perfect difficulty. The graphics are great; some player faces look odd, but the stadia are pretty good. The star-players are an interesting innovation. The commentary is better than it used to be, and if you pick Spanish, you get commentary in that language, not only menus. One big bug, however, is that Spanish commentary quite often makes mistakes on players names.
I miss that the game does not have the “career mode” for coaches. Also, you cannot simulate games…if you take a team through the qualifiers, you have to actually play ALL games. Since qualifying sometimes requires 15 games or so, this may be tedious. Also, while I am enjoying the game more than its predecessors, and my 10-year old is too, his younger brother (who is 5) seemed to have a much easier time with the previous editions, where the fewer control options made it simpler to manage.
All in all, a major improvement.