Alingment is a fine system as long as it's remembered that alingment is based on your characters actions not the other way around. This means that if your playing a lg fighter but in the end you don't want to play a lawful character, you just need to start playing your character differently, maybe come up with a small roleplaying reason for the change (your character in gaining experince has found out that his lifestyle does not suit him, and starts shifting towards a more free lifestyle.) As your actions change a dm should shift your alignment to ng or even cg depending on how you act, and if your actions are to subtly different you can always talk to the dm about wanting your alingment to change.
Some play styles the system isn't good for are people that want to play morally dubious characters and not have a label stuct on like evil even if they rightfully deserve it. This isn't always trying to get away with evil deeds, but it just might be a person who favors shades of gray and then the system might not be right for them.
I have to say that planescape painted two pictures of alingment to me in the same world, one of black and white and the general alingment of the outsiders and planes. But it also painted shades of gray, with the factions who were very loosely based on alingment if at all. All the factions could have people of radicaly different alingments in them on at least one end of the faction. The aranachists I could see having cel members that wanted chaos to reign, and cg members who saw the factions as being to powerful and believed that power corrupts, and was just trying to get the power spread around more evenly. I could see le members of the guvener's (faction based on documenting the laws of planes) who wanted to find ways to exploit the laws of the planes for their own power and lg members who wanted to find better ways to help people, and ln members who were just in pursuit of knowladge.
The alignment system does put a certain black and white in the game, but the dm has a lot of control over how much black and white. They can have characters of radicaly different alignments working together because they have some common ideal even if for different reasons. They can protray the enemy as mercyless blackguards who want to kill as many people as they can, or misguided people that want whats best for a certain group even at the expense of others. They can have all orcs be inredemably evil, or the majority just be neutrals struggling to survive in a harsh society.
Sorry about the rambling so I'll just sum up my point. The alingment system is only what you make out of it, no more, no less.