Is the Warlock good/fun/balanced?
Yes and no, in the same way that most classes can be fun or overpowered if played by an intelligent or crafty player.
From my experience with the warlock so far the two most important considerations when asking if a warlock should be allowed in your campaign are:
1.) Am I ready for the use of the warlock's invocations because of their at will usage?
2.) Should I be concerned about a “un-typed” magic attack that hits a creature's touch AC and delivers a decent amount of damage without a saving throw?
IMO, the warlock is a very advantageous class, its combination of at will spell-like abilities, invocations, touch AC no saving throw ranged attacks, damage resistance, self-healing, armor choices, at-will metamagic, and cleric/monk BAB progression make for a great combination. In addition, I believe that the warlock's often less mentioned ability to create and use magic items from any class is a very powerful ability.
I have yet to play with a warlock at higher levels but I believe that they shine at lower/mid level and equal out at higher levels where a fighters/archers multiple attacks and feat bonuses and a cleric/wizard’s powerful spell selections will equal out or exceed their damage and exacerbate their lack of utility respectively.
Also, there were several mentions about the warlock vs. golems in this thread. In Dragon Magazine 332 "Sage Advice" it says that
Q: Does an eldritch blast cause half damage to constructs?
A: A construct is a creature, not an object, and thus suffers normal damage from the eldritch blast.
And in reference to golems -
Q: Are golems immune to the warlock's eldritch blast?
A: As it is a spell-like ability that allows spell resistance, golems are immune to the warlock's eldritch blast.
