I ran a five-player group through the first part of Doomsday Dawn this Saturday. The age range of players was 40 to 60, with well over a century of collective tabletop-gaming experience in the room. The party composition was dwarf cleric, elf ranger, human fighter, elf rogue, and dwarf cleric. A little more variety race-wise could have been warranted. The group is accustomed to gaming together and synergizing their tactics.
Encounters: The group slew the sewer ooze effortlessly, breezed through both goblin encounters, cautiously avoided the centipedes and fungus, found the idol, battled the quasits for a few rounds, took swigs from the purified font, missed the skeletons entirely, got hit by a pile of rocks, and smote Drakus the Taker in the second round of combat. Only two of the five PCs sustained injury in the double digits; no one dropped to zero at any point. By the last encounter, the cleric had exhausted his channels, although he was very generous with them throughout. Obviously, a four-player party (or a party without a healer) would have been challenged to a greater degree.
Combat Mechanics: The group quickly fell in love with three actions per round with the potential for Athletics "maneuvers" minus the AoOs. Three actions seemed to make combat move swiftly. PCs could get to the front line or get the requisite weapon out and attack in the first round rather than the second. Similarly, the four degrees of success were a big hit. The crits were potent, but in a good way. Even though encounters were generally easy, having random spikes in damage made combat exciting. PCs using ranged strikes were pleasantly surprised to fire into melee without penalty. The lack of a surprise round was noticeable with mixed opinions on its prior usefulness. A few at the table balked when the 1st level ranger's animal companion hawk meted out 1d6 for a beak attack, but we explained it as the bird going for vitals.
Skills: This group uses skills quite frequently, particularly knowledge checks. Finding the correct skill was somtimes difficult. A more detailed go-to list of equivalencies would help. For example, when attempting to assess the construction of the ossuary we lacked engineering and fumbled a bit to find an analogous skill. Also, we're no stranger to hidden rolls. Sense motive and Perception have been hidden rolls for some time. But, by the end of the four-hour session, as a GM, rolling so many knowledge skill checks in secret was unnecessarily tedious. On a similar note, our rogue was bested by a lock. We guessed higher level rogues would meet with less abject failure. The table here was also divided. Some embraced the series of checks required; others saw it as needlessly fiddly.
While not truly a skill, this is as good a place as any to mention our observations regarding the 20' torch/light rules. Four out of five at the table wholeheartedly embraced the lack of an additional 20' of dim radius, arguing that these parameters now make the darkness of a cavern or dungeon a genuine force at the table. Who has the light spell, someone strike another torch, and don’t let it go out were real concerns that heightened the sense of danger and mystery. The other side of that coin was that darkvision is now considerably more potent, a factor effecting racial balance that may or may not have already been accounted for in game design.