The Bigby's spells were completely rewritten. When I see casters using the same spell over and over again on virtually every creature, I know the spell is unbalanced. Bigby's is definitely one of the worst for that. Undead to death is another one.
However, I should have explained the mechanics of the new Bigby's versions so that the casters will know how it works and use it accordingly. I tested the changes extensively with a level 60 mage and felt the spell was working appropriately, but since all the Bigby's spells call the same script now for a resistance check, it's easy to tweak it further.
One of the biggest differences now is that all of the Bigby's spells can be more effective against certain creatures. The only one that really irritates me is the one where you can knock the monster down. I haven't yet figured out how to stop the monster from getting up, walking closer, and then laying back down next to the mage. I'm assuming it's something in the monster AI scripts which take a lot of work to alter.
However, you'll find that nearly all of the Bigby's are better than before in that when you hit with them, they do substantially more damage per round. One of the other ones cuts the opponent's speed way down and gives the monster -10 to hit (the old version--pretty much useless--only gave the "to hit" penalty, but the monster ran after you at full speed).
The first thing the Bigby's script does is run a magic resistance check. If the monster rolls magic resistance, the spell fails. In the past, monsters would get a magic resistance check every round. The new version only rolls the check once when the spell is cast. Caster level and spell level improve the odds of beating magic resistance.
Then a KT version grapple check is made. The caster roll is a d20 plus ability modifier plus a level bonus (max +5). The creature rolls a d20 plus strength modifier plus creature size modifier (ranges from -10 to +10 based on creature size).
Accordingly, high strength and very large creatures are going to be very difficult to restrain with a Bigby's. Humanoid sized creatures with moderate strength (about equal to the caster's ability modifier) are held better than half the time (if the magic resistance check fails). Small and/or weak creatures should be very easy to hold.
As I noted before, I'm still in the process of changing monster ability scores so that 60 is about the highest they'll ever have on any ability. A dragon with a 60 strength would roll a d20 + 25 + 10 = 36 to 55. A level 60 caster with a 40 intelligence would roll a d20 + 15 + 5 = 21 to 40. That seems pretty reasonable to me, since dragons, giants, and other creatures significantly larger than adventurers should be pretty difficult to hold.
A humanoid creature with a 30 strength (typical for the highest dungeons) would roll a d20 + 10 = 11 to 30 versus the caster roll of 21 to 40, giving about a 50% chance of success (not counting the magic resistance check). Once held by Bigby's the creature is pretty much finished/dead.
In PvP, a level 60 caster should have the same ability bonus as a level 60 fighter, they are the same size, and the caster gets the +5 level bonus, giving the caster an advantage.
Again, I think the new version Bigby's are reasonably effective. I spent quite a bit of time testing them to ensure they worked as I wanted, but I understand this is a complete change from the old Bioware versions. The new version is also less effective than I ultimately intend, until I finish reworking the rest of the monsters.