I spearhead the effort to run the new classes in my regular group, our analysis is far from complete, but as the beta is arriving shortly, I thought I'd post our thoughts right now.
Aside- My group consists of six regular members- two of which can only be present every other week- so I am running two very different campaigns- one urban-styled campaign on the weeks everyone is present and a Zelda-inspired dungeon crawl on the weeks there are only four of us. This puts us in a rather good position to use many PC's (Each campaign consists of 5-6 PCs, eleven total)and to place them in a number of contexts- unfortunately it's all rather low level- between 3-5, so it is by no means thorough.
I'll analyze by class:
Cavalier- I'm the only one whose interest was really pique by the class- I think this may be due to the necessity of the mount. You see, as many know, a mount cannot be used in many circumstances, and my players would not want such an important class feature to be so...situational (non have played one yet, but all agree that they'd prefer the weapon option for Paladins and would use non-mount companions when using a druid or ranger). I should say, however, that none of us are too keen on the idea for a replacement option, as a mount is so tied into the cavalier concept. The fact of the matter is, my players have long since abandons the idea of a mounted knight, and have moved on. But...I have played several cavaliers as enemies, so I can report for them. I rolled up several UN-optimal cavaliers- goblins, who I might add were without their mounts. This didn't stop them from putting the fear into my player's hearts. You see, the three cavaliers won initiative and all chose the same character as their mark, and all charged with their small longswords for 2d6+1 damage. Two hit, one criticaled (not multiplying the challenge of course) and killed the level three character. So, the cavalier does have some tricks and- especially at low levels, that challenge can really boost a unit's damage- especially if the cavalier is small, like a goblins were. One thing everyone noticed- the oddness the oaths, we all thought that consistent rulings and less vague wording would help this really flavorful concept.
Oracle- This is the only class to have a PC as it stands right now. The urban campaign lacked a healer and needed one, so I let who ever agree to play the oracle roll one up as a second character. Well, here's the thing- level one (and to a lesser extent level two) cleric spells are not exciting and it makes matters worse when you have a limited amount of spells known. It's no secret that the cleric has a much more situational spell list than a wizard, and being spontaneous just makes the problem more obvious. Now, that isn't to say that the class isn't any good- it fine as a class, it's just the fact that divine characters don't really get fun until higher levels. This class didn't excite me as much as many of the others (I think that it's due to the fact that it's not as "new" as the others-it's more a a sorcified cleric than a brand new concept), but I really like allot of the class features- if I every play one, I'll just do a "House" impression and take the lameness curse. This class is good as is (it really needs more focuses though.)
Witch- haven't playtested this, but it will be used- I was never happy with the options available for a fairy-tale witch, and this seems perfect. Several of the hexes are too weak though (the flight one's duration is sad, and the charming one is weaker than a diplomacy check) I love this class
Summoner- Everyone loved it as soon as they got the concept to the eidolen, for obvious reasons. We've since come to terms how it is less than balanced by doing some math. One player did a one-off character with this class- it totally overshadowed the rest of the party. We love it and hate to see it nerfed, but in our hearts we now it kinda needs it.
Alchemist- I'll find out what this plays like on Sunday, a player's ditching a monk to play one. Oh man was this class love at first sight for him. I believe the line "The alchemist’s reputation is not softened by his exuberance (some would say dangerous recklessness) in perfecting his magical extracts and potion-like creations" sealed the deal. I mean the glee was palpable. This did not dispel my worries that the class might not really live up to his expectations- I told him he could vital strike with the bombs, So If that colors the play-test, sorry, but this class needs work (in ways that many are already aware of.
Inquisitor- No one's playtested this one yet- which is unfortunate, as I rather like this class.
The Alchemist I'm playing in Council of Thieves is probably one of my favorite characters. Him and the fighter deal the majority of the parties damage. Being able to consistently deal 2d6+7 with a direct hit vs. touch AC or 9 damage with the splash has really taken a toll on enemies at level 4. Extracts are more of a bonus then they are a huge benefit of the class so far. I just hand them around as free potions essentially. I'm the party healer with a Wand of Cure Light Wounds and my ability to make extracts of lesser restoration help with all the ability damage. I mainly use Mutagens now for the +2 Nat armor and +4 hit points during big end of the day fights.
CoT is an urban based AP so I've actually got a pottery/alchemist shop setup with my masterwork alchemist lab where I can craft all my goodies and I've really been working on boosting my Craft (Alchemy) so I can whip out a single dose of a poison in a day or so.