Garretts revenge was bad. Really really bad. When I was reading that this used the same map, I was expecting it to also be awful.
It isn't. It's a huge improvement on the original, almost all my complaints were addressed. There are varied textures throughout the mission, all doors are now openable, and intended to open, and you no longer murder an innkeeper.

Errand boy, is in fact, for all intents and purposes, completely seperate from the original mission. The city layout is the same, but that's about the only thing carried over. All the areas are expanded, reworked, and improved. New buildings, new objectives, new everything.

Taken on it's own merits, this is a keyhunt mission. A keyhant mission with a grand total of 11 keys to find. Unfortunately, the mission climbed out of one bad idea filled hole, and immediately jumped straight in another one. But on the plus side, the keyhunting is relatively easy compared to most of the other examples I have seen in this subgenre. It's not to my taste, but most of the keys are signposted well enough. The brushwork in some of the areas that are ported from the original is a little poor, but the texturing is absolutely fine. The only slight oddity caused by the conversion to T2 is the combined hammerite/mechanist force that is now present, but I don't think that's an issue, just a bit strange.

The plot is a bit awkward, with the intitial objective (and presumed main plot) quickly getting sidelined by Garrett learning about a bankvault. As a result, most of your time is spent on what probably feels more like the B-plot. But that makes some sense. Garrett is a thief, of course the big robbery is a bigger deal than the keepers.

The gameplay on expert is too hard for me. This is warned about in the missions description, so I dropped the difficuilty to hard. With that in mind, I found it slightly challenging in places, and generally at a decent level. The keyhunting got on my nerves near the end, and there is a slight issue that vital information is found in notes that Garrett inexplicably DOESN'T pick up. (The vault security information being the most obvious example of this) It seems like such a weird design decision that serves no purpose other than to provide busywork for the player. Either with the player backtracking, or writing notes to themselves. I would say it was a decision to reduce clutter, but this mission is full of inventory clutter. Explosive barrels, notes, paper, a random meat-cleaver, Garrett can't stop picking up everything... except the paper relating to the objective.

Meanwhile, the actual process of exploration is a blast. the city is full of hidden corners, little secrets, and semi-secret enterances to all the buildings. Honestly, the whole place is just fun to immerse yourself in. gaurd density is very high, but not so high it's unmanagable.

All in all, this mission is not a rerelease. It should be treated as it's own thing, and as such I found it suprisingly enjoyable. Still not incredible, but a far more solid entry than Garretts revenge, only brought down by it's keyhunt nature.