The Real Problems Did Not Get Fixed
But let's talk about these individually.
Multiple Attribute Dependancy
Also known as MAD, this has plagued the poor Monk for ages. Monks need Strength for accuracy and damage, Dexterity and Wisdom for their armor class and two saving throws, Constitution for hit points (to be fair, all characters want this) and their last saving throw, Intelligence for skill points and Charisma to make use of their short list of social skills. This is not a good thing, because there's only so many high or even mid ability score numbers to go around. Pathfinder seemed like it was going to help this when it improved the skill system, consolidating many skills and relieving the reliance on Intelligence, but then it turned right back around and made boosting your ability scores with items more expensive, actually worsening this particular issue.
Anti-Synergistic Class Features
This just straight-up didn't change. Many of the Monk's class features are mutually exclusive with other features, with the use of feats, with the use of skills, or some delightfully awful combination of all three. Additionally, Monk still has problems making use of combat maneuvers (due both to low numbers and the increasing Size rating of stock enemies) and the feats relating to those maneuvers got weaker, cutting off a theoretical avenue of contribution.
More Melee, More Problems
Traditional problems with "mundane" or "melee" classes like Monk, but also like Fighter or Barbarian, were not solved by Pathfinder. They still have problems with enemies of all kinds that fly, burrow, teleport, cast spells, use "lockdown" effects like paralysis or poison, and utilize battlefield control (spiderwebs, choking fogs, etc) among other things. Like all melee classes, the Monk is forced to funnel enormous amounts of cash into meeting the increasing demand for complexity as levels and challenge ratings climb ever-higher. Unlike other melee classes, Monks cannot shore up their "primary" role, because...
Monks have no specialization
And, unlike Rogues or Bards, Monks cannot be made into competent generalists because of the aforementioned anti-synergy and low numbers, forcing them to pour resource after resource into badly mimicking another class's role.
On Monk's defence: the Archetype system
Pathfinder did introduce the Archetype system, a refinement on the idea of Alternate Class Features from 3.5e. Some Monk archetypes, such as Zen Archer and Hungry Ghost, work to alleviate some of these issues. Combinations of archetypes, done intelligently, may make for a playable character whose class still reads 'Monk'. Whether or not such a thing is worth the effort is not easily decided, but the options are available.
Monk changes very often
With that in mind, a word to the wise - Pathfinder gets errata often, and Monk has been the subject of many heated debates and quick rules changes, such as the brief-lived errata to Flurry of Blows. This does not have to affect your table, but if you're participating in a sanctioned table (like in Pathfinder Society) or if your group cares about such things your Monk may find the rules shifting out rapidly from underneath him. Caveat emptor.