In the most recent World Cup tournaments, FIFA have gone with the "groups of 4" set-up, followed by the knockout rounds that feature 16 teams. WC's in 1998, 2002, and 2006 have the top 2 teams advancing from each of 8 groups, with a total of 64 games to be played. Here's the question--is this a good format or not? I think it would be interesting to try 4 groups of 8 teams, with the top 2 advancing to the quarterfinals. You lose the round of 16, but each participating team gets to play 7 guaranteed matches instead of 3. 64 games would still be played in this format. So, what say you?
You're going to end up with too many meaningless matches under that format. It would be nice to see a few more of the bigger nations meeting in groupd play, but the length of it would almost certainly rule out any shocks in terms of teams advancing.
For a start the tournament will last three games longer, so two weeks less of a pre-season. This can never be a good thing. After a few games many teams will be eliminated, so teams who need to win to go through will end up playing against teams with nothing to play for. Also there will be less surprises. Group stages can be boring if they're not over quickly, for example the CL group stage is like watching paint dry. A three-game, one-week group stage is short enough to be interesting whilst long enough to reduce randomness.