Here are a few things to consider :

Tactics

If a full attack is "all" it takes to down someone, force Move actions. Could come from cover/concealment or combat maneuvers like Trip/Knockdown or Disarm. If you just play "rocket tag", you're implicitly accepting that if you miss, there's a good chance you're dead.

Note that this is exactly what happens IRL between powerful forces in a battle and in this respect, is not a "bug" of the system but a simple truth.

Intelligence

So you're targeted by a Master Ninja, who manages to sneak up on you and place a Death attack. Curse you, Hayabusa ! Wait, you made your save ! Time to grab your trusty bow and fill him with arrows...
Well, boo. The ninja has broken/stolen your bow as well. Not only does he make his escape, he's slowed you down by forcing you to have it repaired / replaced while you try to get it back.

This goes a step further in Tactics, and is to be expected of Ninja, for example. Study your target. Know their strengths and weaknesses as well as yours. "That Brilliant Bow of Badassitude could be a problem if I must escape. Can I get rid of it ? What about impairing the bowman ? Maybe I could blind him ?"

As an aside, the GM should make sure the players don't feel cheated though. Extreme competence is assumed as part of the characters (especially past level 10) and robbing them of that can be frustrating to no end for some.

Numbers

So they can take the Big-Ass-Monster down in a round ? What about 10 Medium-Sized-Nuisances ? One by itself could barely hope to hit them, but with flanking, teamwork feats and simply being all over the place, the little pests could prove to be annoying. Add in a Leader-type and you could even be worrying your characters.

Story happens

Take the characters down a notch or two through Story. Have them stripped of Rank and Privileges by the King or even make them straight Outlaws. Have them stranded on an island (and some of their equipment lost to the sea) after their boat got caught in a storm. Have their home base attacked (and their Mentor killed, leaving them unable to progress in their main class) while they were on mission.

Change focus for a while

Once all is said and done, if the combat has become so easy it's boring, it may be time to try a little courtly intrigue for a change. Or why not a mystery ? Possibly meshing with "Story happens" above, there are plenty of opportunities to take the players / characters out of their comfort zone while staying true to the setting. They'll be happy to resume bashing heads once they've stumbled for hours finding a tangible threat to pounce on. Or hey, maybe they'll actually enjoy trading piques with the Jester and decide they want a piece of land and a throne of their own ?

You Can!

If a character possesses an alignment that's Lawful Good, one step away on each axis means as a far away as Neutral for the Lawful component of Lawful Good, and as a far away as Neutral for the Good component of Lawful Good.

Here's the chart of alignment steps. While the text reads

that diagonal "steps" count as two steps. For example, a lawful neutral character is one step away from a lawful good alignment, and three steps away from a chaotic evil alignment.

the feat Improved Familiar reads

You may choose a familiar with an alignment up to one step away on each alignment axis (lawful through chaotic, good through evil).

Emphasis mine. Neutral is one step from Lawful on the L/N/C axis while Neutral is one step from Good on the G/N/E axis. Thus taking both steps along both axes allows a LG character to select a N improved familiar, despite the text's 2-step diagonal rule.