That's an unusual playstyle.
Parties offer a greater challenge. Monsters usually can't keep up with a party with four actions and four minds working against save for perhaps dragons.
No, I don't. When I design NPCs, I go for simplicity, plus style.
It's very important that I challenge my players. I spend a great deal of time planning enemies to challenge them from the spell tactics, to feat schemes, to magic item optimization.
I didn't say it gave me problems, I said it took more time. Typically, I had about five books in front of me prepping for a 3.5 game, now I usually have three: the core book, the Bestiary, and maybe one other source I'm converting. Plus, all the new feats are presented in the core feat chains, which makes it really easy to prep NPCs (see above).
My prep has been even easier now that Pathfinder put their entire ruleset online on a single document. I usually have one browser open with several different tabs I click through.
Even then, it wasn't much of a problem... until you wanted to advance a monster who may or may not have spent points on cross-class skills, and whose skills may or may not include an ACP penalty for a shield.
Much simpler now. I didn't much like using the table for different monster type advancement with base guidelines for how to do so. Now I use either the advanced template or I make up the monster as I see fit. Makes it much easier on me.
Fighters do not get sneak attack. They rarely have the luxury of sinking most of their ability score bonuses into a single stat (Dex). So, yes, the fighter's first attack is basically an auto-hit in most battles, at high levels... giving them parity with the wizard, the invisible rogue, and the buffed Cleric. Another way to look at would be that using the new Power Attack, their BAB remains the same while their damage goes up. The fighter has always been the prince of melee control, but their damage has tended to lag. That has been remedied. And while I would argue the fighter has always been effective, having his own bonuses creates more of an appearance of being self-sufficient. It also helps the party, by helping melee and ranged numbers be closer to expected ranges for opponents, even when buffs fail or are unavailable.
To me, increasing a fighter's damage to where they can actually do some serious damage to the giant, rather than just tie up the giant's AoOs, is not a radical increase in power, it's just a courtesy to the guy with the flaming two-handed sword who wants to feel good about themselves as they are smacking the bad guys.
For certain Dex builds, the Pathfinder fighter might be decidedly superior, but otherwise I think you are talking about a 25 to 30% increase in damage, even taking into account situation advantages.
I find sneak attack situationally useful and easy for intelligent monsters/NPCs to counter, especially at higher levels where monsters and NPCs can see through invisiblity fairly easy. And most wizards don't like to waste their spell slots casting on the rogue.
Even if the rogue buys greater invisibility scrolls and uses them with Use Magic Device, the fighter has most likely already engaged a creature. And by the time the rogue moves into position for his first sneak attack, the fighter has the creature almost dead or dead.
I have no problem with what they did with the figther. I don't agree that the fighter isn't amped up though. 20 to 30% extra damage is most certainly amped up. And the ability to stun (very powerful) and cause serious negative effects to enemies with criticals is very powerful. An average high level hasted fighter gets 5 attacks per round. Chances are he is going to crit with one or more every round causing some type of effect that if optimized (usually stun, daze, or blind) is going to pretty much make the fight hopeless for whatever he is fighting.
I've been in a heated debate with some others on this board over fighter vs. wizard power. In my own experience, fighter-types have ruined more of my carefully planned encounters with crits than wizards or clerics.
I can plan for wizards or clerics. Magic in general always has a counter or high spell resistance can generally throw off a wizard or cleric.
Nothing really stops a lucky crit. A lucky crit with a greataxe or other x3 weapon is nigh encounter ending for all but the toughest monsters. With the fighter boosted, he is a crit machine. I have yet to run a fighter at lvl 20. But further boosting his crit ability looks like it will be a nightmare.