The warlord is AMAZING... if you have a full group. His ability to shift his allies into combat advantage positions and take attacks on his turn, even at first level, is incredible. He can literally shift a nearby rogue friend into flanking a monster he's facing, then attack that monster with the flanking bonus. Then the rogue can attack, without moving, to get his 2d6 or 2d8 sneak damage. And that's just an example off the top of my head. There's even a power that let's him attack, then let one of his allies attack the same monster with a Charisma bonus to the allies damage. That poor kobold skirmisher won't know what hit him.
The warlord's powers are great, but so largely situational as to almost require another another melee character or two to work in concert. A two player warlord/wizard team would be virtually worthless. At least from the few powers I've looked at so far. And trying to use a warlord as a fighter would be equally unfortunate - his power lies in manipulating his allies movements (voluntarily, it should be noted) to incredible benefit.
That said, I'm not sure how much benefit groups who play gridless 4e will get from a warlord.