Power Attack is generally considered a good feat because of the reasons listed, and also because there are a lot more ways to pump your attack roll than your damage roll. You will find yourself missing a lot at lower levels, particularly if your DM doesn't understand the encounter building rules, as weirdo referenced above. But more particularly, it seems like your DM doesn't understand the rule that the game is about the players, and they don't want to be dragged around by the DM's superhero :)
The core rulebook has plenty of rules to be effective and have fun. There's some cool stuff not in there, but if you're still getting to know the system, what's good and what's not, it's a decent idea to limit your options. Maybe go Core and APG, but don't just use anything under the SRD sun if you aren't comfortable with what most people consider the "basics."