I've seen most of the new classes in play, though not always to high levels. Here's a few notes:
Psion: It is amazing how often monsters will save against Mind Thrust and the Psion is left there doing nothing useful! As this PC is only 4th level in my
Mark of Heroes game, it's hard to say exactly how useful it is, but the player enjoys it, and it was extremely effective last session.
Psychic Warrior: As the PC was multiclassed with the Pyrokineticist, I didn't see much of the PW. The PK was very effective, though. And death on any curtains that happened to be around.
Soulblade: They don't like ghouls. One of the more challenging classes - fun, but just slightly underpowered. I really suggest playing a Kalashtar Soulblade with the substitution levels from Races of Eberron.
Favoured Soul: My favourite take on the spontaneous divine caster. I've seen them played at levels up to about 10th, and it's a fun, useful class. It shouldn't go charging hydras on its own, though. (It's best when combined with the Revivify spell from MHb). (It is also significantly more enjoyable than the Mystic from DL).
Spirit Shaman: Definitely an oddity. I'm sure I've had one in my game, but I can't remember anything more. Perhaps it died after one session. That seems likely.
Swashbuckler: Relies somewhat on having a campaign that makes use of its skills - especially Diplomacy. That said, fit right at home in my Eberron game, and also was great in the "Renaissance Greyhawk" game I actually got to play in! Doesn't do so well against constructs, as the Eberron character found out when he got squished in the finale of Grasp of the Emerald Claw. I think it's a well-balanced class.
Samurai: Somewhat misnamed, but a striking class. I've got one being played in my Necropolis game at the moment at 12th level. Very effective melee combatant, with high AC, hp and weapon damage. Switches between two-handed and two-weapon fighting depending on opponents.
Hexblade: A fascinating class. The arcane antipaladin in many ways. This is another character being played at 12th level in my Necropolis game. The combination of good attack, AC + HP and "the curse" has been most effective. Definitely holds its weight, despite the PC having died and been raised three or four times. (A problem with being in Necropolis!)
Warmage: If you need something blown up, this is your man (or woman, as was the case in my game). I'd go batty trying to play something so focused (I play generalist wizards for a reason!), but there's no doubt that it's effective at what it does. Great for players who just want to kill things.
Warlock: I'm not so fond of this class as a PC, but it is *the* evil manipulator NPC class. I use it as a recurring villain in my game, and it is effective and annoying.
Scout: You need to have a good player for this class. I haven't seen one played really well yet, but I'm likely to once my Ulek campaign gets going. The recent errata to the class (adding Disable Device to class skills) makes it a suitable replacement to the rogue. I've seen both the archer and spring attack versions of the class, and I do like it - I'm interested to see what lies ahead for it.
Ninja: One of the most evocative and fun classes Wizards has come up with. Who doesn't want to play a ninja! (Well me, but anyway...) It's an effective class. It doesn't have quite as strong a melee attack as the rogue, but the invisibility gives it defensive abilities superior to that of the rogue. Very good.
Artificer: If you have warforged in your party, you need one of these! Great class, although possibly broken with a couple of feats/infusions being much stronger than you might expect. The ability to give a weapon "bane" has really made this class effective, but I haven't seen one played at high levels yet.
Cheers!
