Playtest conducted at level 9. Samurai is Human. His feats include Step up, Following Step, Step Up and Strike, Vital Strike, Power Attack, Imp. Trip, and Weapon Prof. Meteor Hammer.
Other players in the party were a Gnome Cleric of Sarenrae, Human Druid, and a Halfling Ninja.
The Samurai found himself going solo for a few rounds because of a failed Perception check. Basically he got nailed with two rounds of sneak attacks from a roguish robbery attempt.
He was going up against 4 roguish types that got the drop on him. He suffered over half his hit points in sneak attack damage before he even knew what was going on.
The villains were doing fine until they started trying to adjust for sneak attacks with 5 foot steps. It got pretty ugly after that. They lost two of their number to vicious katana strikes before the cavalry came to help him out.
The Samurai did an average of about 30 dpr, and he didn't even activate the Flaming burst quality on his keen weapon. He didn't have to use any of his special abilities in this fight, but not a bad warm up. More to come when we play again.
Looking through the samurai's abilities it is hard to imagine them dealing a lot of damage. They are steady at it though.
I'm playing a figther 1 / samurai 3 and he is durable. Fatigue, sickened, fort saves, will saves, negative hit points, these things don't stop the samurai. Sure I'm not constantly turning invisible like the ninja, but the hits he takes keeps the party from being attacked. A Power Attacking katana strike every round is nearly as effective as the two rogues' sneak attacks.
I wouldn't mind a feat like Extra Resolve (Begin the day with 1 additional resolve point). I don't like the fact you have to finish your challenge target to bring it back, but we just hit level 4 so maybe 2/day will make it a bit easier.