This probably won't satisfy the truly hardcore professional and pseudo-professional game designers, but we've been wanting to contribute to the playtest, so here's the little bit we have.
I don't have details on any characters, but it was an all-tenth level group built for a one-shot encounter. Human cavalier, half-orc cavalier, human oracle, gnomish summoner, human inquisitor.
First off, I've seen a lot of criticism about the over-powered potential of the eidolon and I have to admit that I was able to design her as a meatgrinder fairly easily, but I felt that there were significant trade-offs between offense and defense. A magical opponent would have eaten her lunch -- or used her to eat the party's. I'm sure the optimizers can do better, but for a little time outlay, I was pretty happy with her performance. Bipedal, Large, Extra arms, Claws, Reach, Rend. She did 98 points of damage in a single round to a stone giant -- I don't get to play with those kinds of numbers often, so it was great! (Never mind that said giant only had 8 hp left, that's not relevant.)
Both encounters were unknown going in -- the party was asked to investigate a terrible story provided by a survivor who didn't live long enough to give details -- classic vanilla hook.
In the first, we had not done much buffing when the human cavalier decided he didn't need to until he'd seen what we were facing -- and took a thrown rock in the chest for his trouble. We faced a stone giant and his two pet dire tigers. Our cavalier had the special ability to take some damage from each hit as nonlethal -- he was unconscious before the second round was over. The eidolon was enough threat that they didn't finish him off -- they turned to her and the other cavalier. The summoner and oracle primarily served as support -- buff spells and healing -- and the summoner never even used his SLA, though he could have. The inquisitor buffed himself and used greater invisibility, only to get hit anyway by a dire tiger when he attempted to approach, and never even got to attack -- the foes were all dead inside of five rounds. Might have been four, I'm not certain. Overwhelming victory for the good guys and a lot of fun was had.
Since we wrapped that up so quickly, the DM grabbed the bestiary, said reset your abilities and hit points, etc. for a completely new day, and proceeded to use the same map as a battleground for five stone giants. The only change (he says) from the bestiary was giving them all +3 weapons so they would hit our higher ACs better. This one was a fight - the eidolon essentially went toe-to-toe with two stone giants (one at a time) and was down to a single hit point when she tore the second one in half. She had some assistance, but most of the attention was with the human cavalier again, who had charged a giant (in the dim light) not realizing that he would end up within reach of three giants. He was down to 3 hp and his horse was killed before the tide turned. The other cavalier did not survive the first round. The summoner used his SLA to bring in a bralani -- an awesome addition to the summon list (or new to me, anyway) and one that I played terribly, I'm sure. Other than that, the summon was casting buff spells and trying to keep his eidolon alive. The oracle's healing and the bralani were key in my mind -- mass cure light wounds (and the bralani's healing and mobility) kept the human cavalier alive (and the others tip-top) while the others got into position to do some damage to his three playmates. I completely overlooked the bralani's DR until it was over or he would have been much more of a force to reckon with, combat-wise. At it was, he was able to use lightning bolt and hit three giants each time. Glitterdust from the summoner gave the cavalier a short respite as his foes couldn't successfully target him. The inquisitor, hasted, nearly took out a giant by himself once he got into position. The oracle also did some ranged softening-up using searing light.
All in all, I think it was a success and I did not hear any significant concerns with the characters. Since we're not a hardcore group, we don't analyze the tactics and abilities to the nth-degree and didn't have all our buff spells pre-planned and synchronized, but we were able to utilize a lot of our class features without a lot of homework.
I guess I'm saying that the classes were usable, they each have a flavor that is their own, and they were very playable, even by a casual group like ours. The one concern I heard was regarding the cavalier's dependence (in that player's mind) on being horseback.
Hopefully there's some useful feedback in there. I did not try to record a lot of details beyond the information provided here, but if there are questions, I will try to answer to the best of my ability.
(Oh, during the fifth-level playtest using the original beta rules, we faced a pair of bearded devils and their pet hell hounds. That was very tough, but we persevered with one devil teleporting away from certain defeat. Also very fun.)