My experience has been that a good group can make just about any system fun. And, similarly, a bad group can ruin the best system.
That's why I said that a bad system sucks the fun out of a group "slowly but surely" and a bad group sucks the fun out of a system "faster than a speeding bullet".
A good group can make just about any system fun, but the effort of making it fun (IMHO and IME) eventually wears the group down.
I went into 3.0 with a great group, and we had fun throughout our playing, but the looooonnnnnggggggggg combats eventually made some players dread combat encounters. And this is understandable; combat seriously damaged what could otherwise get done in a game session. When the pace of a game suffers, the fun of the game suffers.
Now, I realize that some groups might prefer long combats, and it is great that there are systems out there that do this. And I realize that it is easier for a great group to handle a dull system than it is for a dull group to handle a great system. And I realize that both "great" and "dull" depend upon your preferences, both for group and system.
But, ultimately, my experience is not that "a good group can make just about any system fun", but that "a good group will find a system the members consider fun".
I mean, there's no reason to play (Enter System You Don't Like Here) just to show that your group can make it fun when you have the choice of playing (Enter System You Like Here) instead.
RC