Character creation is that essential and oft times maligned part of RPG's where I find that the designs of the DM and players tend to run perpendicular.
As a DM, I've learned to never start planning an adventure until all the characters have been rolled up and finalized and to be present at the creation of all the characters.
I've come to believe that as a DM, it's part of my responsibility to craft an adventure with my player's characters in mind. While I never tailor create an adventure to the characters, I try to create scenarios where no one feels useless, and everyone can feel important. The idea is for your players to have a good time, and more often than not, happy players mean a happy DM.
My two biggest gripes as a DM about character creation are min/maxing and the question, "What does the party need?"
Min/maxing is the bane of role playing. When you pour all your energy into making sure your character is the strongest, most powerful creation possible, you're missing the point of creating a character, and perhaps, the game. You should strive to create a character that you enjoy playing, not the one with the best stats. How powerful your character is has little to do with how enjoyable the character is to play.
My second biggest grip during character creation is when a player asks, "What does the party need?"
The party needs your character! Whatever class or race you choose should be up to you and you alone. There are no healers in the party? So what? If you don't want to play a healer, then please don't. It is way more important to the over-all enjoyability of the game that each player really like playing his or her character. The game is not about being the most effective "squad", it's about pretending to be someone else with your friends who are doing the same.
When you come at a game like D&D the same way you come at a video game, you rob yourself of the fullness of the experience. If you're a clever player and you have a decent DM, you have almost unlimited freedom to create whatever characters and scenarios you want. A party of nothing but fighters can almost certainly overcome any situation thrown at them.
Ingenuity, skill, and grit can overcome any obstacle, regardless of what classes make up your party.
...and if all else fails, gold works too.
A player should never feel obligated to choose a certain type of character based on what everyone else is playing. I recommend that each player get with the DM and roll up their characters separate from the other players and by all means keep it secret. That first session when everyone meets each other should be nothing, if not memorable.