Draigo and his Paladin Bodyguard (or vice versa): 8 MC Pyscannon shots a turn are nothing to laugh at. They shred light vehicles and even LRs don't like eating that kind of firepower for more than a turn or two. They hold up pretty well against the occasional lascannon/MM shot, but torrents of shots still down them fairly fast without an Apothecary. I still love the unit and want to make it work.
Interceptors: I want to love them, but they are very expensive for what they currently do. The Pysbolt upgrade and the MC on the DH might have to go to make them more affordable. Both upgrades are temptations to either shoot at AV11 or try to take on Dreads (both of which I tried to do in test games). Fully upgraded, they cost almost as much as the Paladin squad, so using them as a simple harassment or sacrifice unit just isn't cost effective. The shunt is simply amazing though. It can be used to hop into a hole in enemy lines or a parking lot, jump out of a bad position, or go for a last-turn objective grab. The tactical flexiblity is great, but it is a yet another pricey unit in an expensive army. I plan on keeping this unit in the list, but trying to strip the points down some.
MM/HF Venerable Dread: Another unit that has been "solid" but overall untested and unimpressive. One MM shot at BS5 isn't terribly impressive on such an expensive platform. The WS5, S10 DCCW is nice, but a DK can do it better and cheaper. The Reinforced Aegis can be useful, but I'm not sure if it is worth it. Overall, I think this unit is probably getting axed.
GKSS: The 10 man unit is a solid block and has done a good job of supporting the Paladins. If they get the chance to anchor in a stationary spot, they can dish out some serious hurt with their Pyscannons. With the full 10 men, I feel confident with them hanging outside of their Rhino during KP games. The 5 man squad, not so much. I didn't feel like they were worth exposing to small-arms fire and risking a KP. In both cases, they are overly expensive to use as screening/charge absorbing units.
Pysflemen: I love these guys... they live up to they hype and then some. Point them at anything AV12 or less and it gets shredded. My only quibble is that I only have 3 Heavy slots for them, which leads to my last unit:
Dreadknight: The DK has performed very well for me. In one game it got to shunt punch a LR on T1 which was basically an autowin. The second game it never even shunted and used its 12" moves to force my opponent to double-back with TH/SS Termies to kill it. This bought me an extra couple of turns to kill his LR and ignore his Termies. Had he not diverted to kill it, the DK would have ran rampant through his backlines. Yes, it can be shot to hell pretty fast, but most armies have a limited amount of high strength AP2 to split between it and Paladins.
Overall, the army has been effective against Mech Marines, but it definately has a lot of weaknesses. It is slow with limited long-range reach and power is concentrated in a small number of units. It has no screening units or movement-blocking units to slow down aggressive assault armies and has only a single MM to handle LRs. I definately plan on reworking it tomorrow.