Last night I inflicted five of the playtest characters against my group, as part of a side-story in my Runelords campaign involving the Runewell underneath Sandpoint.
First, here are my general thoughts: One problem I had was keeping track of various people's abilities. If you're running new classes, it may work better to run one or two rather than five like I did. While I use Hero Labs for my gaming, the poor system was creaking and barely able to handle everything involved. Notecards and the like will likely be of use to keep an eye on what your new classes can do.
The conflict involved my PC group (Sorceress, Eldritch Knight, Arcane Trickster, Cleric with one level of Bard, and Barbarian), vs. a Blood Rager, Brawler, Hunter, Skald, and Slayer. Due to the high stats (rolled) of much of the group, I used 25-point half-orc builds for all of the alt-classes.
First blood came when the Arcane Trickster stupidly entered first, didn't use total defense, and got swarmed by the Hunter's bear, the Rager (with Abyssal so he was fighting with claws), the Brawler, and Tsuto (who'd taken several more levels of monk). She was at -9 HPs, and literally only survived because of a handy AoE heal by the PC Cleric.
From there, things got messy. The PCs were in a choke point, which limited the effectiveness of the enemy AND the PCs. Several things did stand out, however.
First, the spell Strangling Hair? It's horrifying. The Sorceress pulled a Rapunzel and ended up disempowering the Blood Rager, the Skald, and finally caught the Hunter. Mind you, this was over the course of the conflict, but it was still... disturbingly amusing. I mention this because after almost disemboweling the poor AK, the Blood Rager proved... ineffective. Being wrapped up in hair and attacked with a Ranseur while choked by hair does pretty much mean you're not going to get any other blows in.
Don't get me wrong. The Blood Rager was doing +11 damage per blow with those claws. On paper he was a mean lean killing machine. But he didn't get to shine because that Strangling Hair spell somehow has range. I felt kind of bad about it. (Also, he rolled horribly to try and escape.)
Second: The Brawler is actually a fairly decent fighter. He was going up against a halfling with an AC of 24. He still managed to get a few blows in using flurry-of-blows. If there hadn't been a chokepoint, then he might have had a few moments to shine. Either that or if he'd been fighting the Barbarian instead or someone with a lower armor class.
Third: The Hunter proved possibly the most effective character in the group. While I'm still unhappy with spell selection and feel these classes need their own spell advancement charts, the combination of an animal companion and raining ranged death on people had him as pretty much the most effective of the new classes.
Fourth: The Slayer didn't have a chance to shine. This is rather sad actually - part of this was because I used too many classes at once. So I failed to use his ability to study his foes and he never got to sneak attack. The lack of flanking opportunities also hurt him.
Fifth: The Skald feels lackluster. To be honest? I'd almost suggest dropping his spellcasting entirely and beefing him up in other ways. Mind you, the Rage Song did enhance the nastiness of the entire group (Though that was balanced out with Bard Song on the other side, and the Sorceress' ability to boost morale bonuses so the PCs had +2 to their bonuses instead of +1), but I'm not sure the spells fit him. With the limited selection of Rage abilities with his Rage Song, he's almost a support role. This shouldn't be the case. He should be in the front, singing the glories of Odin as he smashes a warhammer into the faces of his foes.
If anyone wants, I can include builds for each of the classes.