@KRyan let's define low levels as 1-6. that would be 1-4 feats, and yes, you are only shooting for the ones absolutely fitting your concept (and get 95% or even 99% of overall feats ignored, not just bad ones). While you are right that decision tree gets pruned really fast leaving only a handful of best feats to consider, this "best feats" set is obviously different for different character concepts, which is the fact you seem to overlook.

@KRyan but yes it does. If we're talking core only, weapon focus is a decent feat - not the best one, but I would be perfectly okay with taking it in certain circumstances in core-only game. It gets significantly worse when you add splatbooks to the mix, because of sheer quantity of clearly better options.

As for Combat Expertise or Point Blank Shot, they are certainly viable. Combat Expertise is a prerequisite for Improved Trip AND is actually used with the trip, since it does not affect trip check and touch attacks tend to hit anyway. Point Blank Shot is a prerequisite for a number of good feats (Rapid Shot among them), and +1 to atk/damage is nothing to scoff at in a game where ranged character has almost no feats to choose from.

Even Alertness can be useful if you're going to max out your perception skills, which is quite difficult in core.

@KRyan this ans the Tome of Battle passage are leering into casters vs mundane territory, which I'd rather avoid until we discuss the matter of the feat quality, since that can totally derail the conversation. But I'm noting the point and have something to say about it.

@JeorMattan "a prerequisite for actually good feats" does not a good feat make; it makes a feat tax. Lack of good options does not make bad options better. If you feel the need to include supplements to accept that the bad feats in Core are bad, then fine, include them. To my mind, those feats were bad from the moment the PHB was printed, even if you did get forced to take them for lack of other options or because of poorly-considered prerequisites.

ignoring the Fighter (a poorly-designed class in any case), and ignoring feat tax prerequisites, a Human gets 4 feats. As far as power is concerned, the 6th-level feat should be Leadership for basically anyone who's not a Druid; then again, Leadership is not what I'd consider a well-designed feat (it's hideously overpowered)

ignoring that

for melee warriors, in Core, you have Power Attack, Improved Trip, Exotic Weapon Focus (Spiked Chain), and Spirited Charge as the best feats available.

for ranged warriors, there's Precise Shot (still taxy, though), Rapid Shot, and Manyshot.

for TWF, obviously you need Two-Weapon Fighting

my Weapon Focus is better than Exotic Weapon Proficiency (Spiked Chain) if you take it for Reach weapons and do not care for the Spiked Chain's disarming and finessing properties.

it is not better than Power Attack, Improved Trip, or Spirited Charge

on the ranged side, Dex-to-damage is better than Precise Shot, but not the other two

so my argument is that while my version of Weapon Focus is among the best feats available, it is not so good that every character ever would definitely take it

though really WF(Reach), WF(Expertise), Imp. Trip, and Combat Reflexes is probably the best play

which, speaking of, I forgot Combat Reflexes in my initial list.

that's a quite-good feat

out of core, you have stuff like Martial Study, Shape Soulmeld, Hidden Talent, etc. for accessing other subsystems in a limited way; those are powerful options

you have high-power melee feats like Shock Trooper or Leap Attack

Craven is better than WF(Sicarii), though of course both are desirable

but basically, my Weapon Focus is likely to find its way into a lot of builds, but it's not the be-all, end-all of feats

and the fact that a feat that was previously an unnecessary tax on melee characters is now a feat that a lot of them want to take anyway, is in my opinion a very good thing

since it pulls double-duty as a prerequisite and as a solid feat in its own right