Problem the first: calling them Rogues instead of Thieves (or Assassins); thus implying there was supposed to be more to them than sneak-scout-infiltrate-spy-steal-backstab.
Problem the second: trying to make them able to do something *every round* in combat. Thieves work best when they get their backstrike in round 1, then spend the next few rounds blending back into the scenery before taking their next devastating attack in about round 4. Failing that, they spend the first few rounds sneaking around the main combat to get at the enemy spellcaster and glue her up...
Problem the third (for those who disagree with problem the second): immunities to criticals and sneak attacks. OK, an undead has no functioning internal organs, but it can still have a specific point that holds it together e.g. a skeleton's spine; and that's what a critical (by luck) or a sneak attack (by skill) connects with.
Problem the fourth: giving them "sneak attack" when they're standing there in plain sight, just because someone else is there too (flanking). Does nasty things to my sense of realism...
Not sure how any of this is solveable. I like Thief in principle as a class, though I've had awful luck playing them; the obvious solution of "dismantle the class and make the skills available to others piecemeal" just doesn't fly with me.
What might make them more playable (in any edition) would be to ban some spells that intrude too far into their niche.
Knock, I'm looking at you.
Also, keep in mind that in pre-3E days Thieves bumped way faster than other classes; this alone served to balance them surprisingly well as they'd often end up a level or two higher than the rest once things got going; with correspondingly a few more dice worth of h.p., better saves, better attack matrix, etc.
Lanefan