I thinks it's hard to play without any of the 4 roles.
I have run a few sessions of keep- 2 rangers (both do d10+5 with each hit of twin strike) 1 ftr and 1 cler.
they are destroying the keep- the twin strikes are basically broken. If one of the rangers was a wizard, the group would be significantly worse.
although, they did skip A3.
...
Party has 6 PC's: Wizard, Rogue, Warlock, Ranger, Fighter, and a Paladin.
....
PS: I can't believe how "swingy" this version is. Not a complaint, mind you. Just seems way more dependant on dice roles, which has been part of the problem for my group. The guy playing the Fighter and running the Paladin when the original player had to go, failed 6 saving throws in a row to stabilize when they were both dropped below zero. And the Fighter even had the Human bonus to saves. Hmm thats not swingy, just bad luck I guess.
Failed to stabilize? You need to roll a 20 to stabilize... 6/20 = 30% chance of that happening.
The whole heal CHA + 1/2 level (and get a save, with a feat) when you spend an action point helps out some, as well.