Two caveats: First, I haven't looked at the rules in depth in a little while. Second, fate conspired to rob me of any time I might have had this evening to look at my book, so I have to go by memory.
That said, the first problem is that the perceived boost to fighter types is somewhat illusory. While characters have ~50% more feats (from 1/3 levels to 1/2 levels), for many things they need to spend twice as many feats for the same benefit they would get in 3.5 with one feat. Improved Trip and similar combat maneuvers are thus more expensive. Furthermore, some of the bread and butter feats like Power Attack and (Cleave? memory foggy) are actually weaker. So while fighter types may feel they have more power, in reality they are more straightjacketed than before.
Second, the problem with casters is that they largely use "I win" spells, from as early as 1st level Sleep. While some of the "I win" spells were removed, others were not, and some new ones were introduced. At the same time, casters were given more HP and additional abilities that either made their "I win" spells more effective or allowed them to focus more on the "I win" spells.
So while the fighter "may" (but probably not) be a little better at dealing HP damage and mitigating HP damage, it is still just as irrelevant as it ever was because the casters are even stronger.
All of this, of course, is IMHO
Cleave was changed to trigger when attacking, instead of when killing. It has to be adjacent though.
So it can be used to make two attacks a round at 1st level
every single round as long as you have two adjacent foes... instead of only triggering when you dropped something.
Personally... Pathfinder's cleave has come up far more often in my experience.
Trip was dumb in 3.5e. It was abusable (straight Str check), and free attacks made it the defacto maneuver to pick.
Now, you have your pick of Trip, Bull Rush or Overrun, and they all make your victim provoke an AoO... meaning it's not a tactical option, because it gives all your allies a free attack, not just you (note that Bull Rush only gives your allies the extra attack).
The APG adds Drag and Reposition maneuvers too (that also provoke AoO), so you really do have a wide variety of choices, instead of "take Trip, it's miles better than everything else".
Besides... needing 1 extra feat for that one particular combat build, vs the 4 extra feats you get over 20 levels... I'm thinking that martial classes still come out ahead.
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Regarding Casters...
The hitpoint bonus was virtually unnoticeable, and was really done as part of streamlining the rules. Casters in my games typically get killed very quickly regardless if they have that extra 1-2 hitpoints at the lower levels, and dying from things other than hitpoint damage at higher levels.
Note, the Ranger was boosted to d10, and the Rogue and Bard got bumped up to d8 too, so that's really three non-full casters that got bumped up along with the two full casters (wizard and sorcerer were the only changes for full casters).
"I Win" spells are using a limited resources to work, and are typically all or nothing, and the casters using them don't always have the right one available for all situations (spell targets wrong save).
A first level wizard casts 2 Sleep spells a day, maybe 3 (if it's an enchanter wizard). If you are facing a high Will save target, (or if they roll well), it's either not used or potentially wasted.
In my experience, the Wizard needs the "unlimited resource" martial character to take care of general things, so that he can pull out the "I Win" ability against the one or two major targets (using a big ability on a big target). Without the martial character there, the Wizard would be wasting his limited resources on dealing with everything up to the important target.
I'm confused about the line "
additional abilities that either made their "I win" spells more effective or allowed them to focus more on the "I win" spells".
The only abilities that the full casters got that I have seen are fairly generic and don't really boost any of their spells (they are typically minor side benefits that don't always fit a full caster... like claws, or reach, with the exception of maybe the Universalist's limited metamagic boost). More flavour than power.
I'd be interested to hear of any combinations that you've found that make the Pathfinder wizard "focus more on I Win spells".