The 4E fighter was probably the biggest source of disappointment to some of my players. The reason being is that 4E made the fighter into something we didn't want. I LOVED the 3E fighter. Compared to the fighter of previous editions, he was exciting. He was customizable and could support a wide range of options; in our game that ran for 8 years (from 1st to 30th) we had three fighters in the group: an archer who eventually became an Arcane Archer (and then a custom class), an archer who became a Deepwood Sniper and a sword-and-board tank.
4E could not accommodate those concepts. When my wife created her fighter, we were stunned to realize that a Fighter couldn't wear Plate. It made the Paladin seem like a better fighter than the fighter. My wife also found the Defender role disappointing: sure the fighter had always been the meat-shield...but that was in addition to laying down the smack. In many ways the 4E fighter should be rename The Blocker or The Threatener...because they don't fight nearly so much as they take punishment. And that's fine...if you want to play that particular role.
To me, the fighter should fulfill his particular niche better than anyone else, and he should be able to do it with skill while not exceeding other classes (or falling behind them). Mostly I agree with Morrus. The 'core-four' should be the template: fighter, wizard, rogue, cleric.
The idea of themes sounds like a good way to allow much of the customization that 3E offered without needing 10 class concepts to fulfill the role. Want an archer? Make a fighter with the archer theme. Want a greatswordsman? Take the Zweihander theme. Want a cavalier? Take the Knight theme...and so on.
A class should be able to be summarize in a single concept:
Fighter: master of weapons and armor
Rogue: sneaks, highly skilled
Wizard: master of magic
Cleric: warrior-priest
The second tier concepts follow on those, with enough flavor and play difference to matter:
Sorceror: mage with less choice, more frequency
Paladin: holy warrior
Barbarian: light-armored warrior who rages
Ranger: woodsman with bow or dual-weapon skills
Bard: jack of all trades, master of none; uses music magic
Druid: shape-shifting nature magic-user
To me, the fighter should be able to encompass a variety of concepts (as it has in the past), whether it be the valorous knight, the precise archer, the monster with a greatsword or the 'mace-o-matic' walking tank.
What I liked about the 3E fighter was his not just his large number of weapons and armor, but the combat options that made his options more exciting. Others see exploits and loopholes and perhaps there were plenty of 'blind kobold' issues to be fixed....but the ability to choose to fight based on more than just rolling a d20 was a welcome change. 4E followed this trend and delivered lots of great battlefield control options, but sacrificed dynamics to do it, IMHO.
I hope the 5E makes the fighter versatile, not limited.