The Chevalier's pretty fun -- though I don't like the static power bonus at level 10, if only because players will forget it's a power bonus and try to stack it (a problem with power bonuses, particularly on things that aren't powers).
The Guardian e1 is hella strong; depending on interpretation you might be able to see the attack roll (or at least the targetted defense) before choosing to use the power. I could see even playing this with a striker with a good basic attack (Avenger, for instance), as immediate action attack = power and the rest is gravy.
Regarding the guarding 10, I think if you look at the examples, it is intended to be used with a PC; they're just trying to avoid having people use it with the defender. Using it on a ranged/area PC (whose overall power might equal your own, but whose -melee- power does not) seems to be the intent; note: "You might be partnered with a wizard or a cleric, sworn to accompany your charge on his or her travels and guard him or her with your very life". Mind, I'd have preferred if they said "your charge must not be a defender or melee striker" or something else less wishy washy then the whole "melee skills equal your own" thing.
Hospitaler: Solid. L5 is rp, l10 is more healing. More healing is good. At l11, you're healing [surgeless] 10+2*wis per encounter. Also, the Ue6 is something people might actually take -- as mobility options are thin on the ground for the defenders and leaders who are most likely to take this theme.
Noble: yeah, kinda weak. The ally move ability is fun, but I prefer ally moves as minor actions, as that means you can move too. But the level 5 and 10 features are weak; a skill bonus and an item. OTOH, the U2 is fantastic (use intimidate instead of bluff or diplomacy every encounter? Yes, please, says the noble half-orc negotiator. ) The U10 is also amazing for a high initiative character, as you get to let another party member completely ignore his or her initiative check every encounter and use yours instead (and if they roll well, you boost someone else instead). So oddly, it's got some of the few theme utilities I might actually take.