After this past year of working on this project and forging our way through the various bugs and challenges, one consistent theme that’s emerged is that the difference between what we have and what we want is clearly visible. When we look at today’s World of Warcraft, we can see the differences between the modern game and the classic one. If we tried to update the reference client, we would have instead been tracking down a lot of “invisible” changes such as exploits waiting to be abused, crashes that don’t show up until you have millions of players online at once, and more. We chose to approach the problem in a way that makes our job clear and obvious instead of difficult and hard to see. 
Finally, a new stat I'm adding to this round-up: the number of moderator actions performed for the past 30 days! We performed ~6,000 actions 60 to 90 days ago, ~11,000 actions 30 to 60 days ago, and in the past 30 days we've performed a whopping ~19,000 actions. That's a lot of permabanned plebs, let me tell you. I assure you, the rumors of power-tripping mods hell-bent on getting our jollies from holding power over an internet forum is really, really true. Especially u/Undoer. But for real, y'all have unleashed the biggest zergling rush of posts and comments I've ever personally had to deal with, and we're a squad of about four Firebats in a bunker with one SCV doing our best to hold this ish down... wrong Blizzard game, but you get the point.

Nov 15 Classic is too easy for 2019 playerbase I'm not big on gameplay changes, really I'm not but... The game is just too easy for today's standards. I really think some of these raids and instances need a serious increase in difficulty. MC is a joke, most of the tier sets are unbalanced, and a lot of seasoned players agree but fear the toxic Classic community to speak up on this issue.Hopera237 Nov 15
Our initial runs exposed a few (expected) issues: the game sometimes crashed, didn’t recognize our modern video cards, and was incompatible with our current login system. That first pass also couldn’t support any of our modern security and anti-cheating capabilities. Clearly we had a lot of work to do to make WoW Classic live up to the Blizzard standard of quality, and deliver the experience players want.
When it comes to Classic, Blizzard's goal is to provide an authentic Vanilla experience, but they also needed to come up with technology to handle many players at launch, which is similar to sharding. While the use of this technology will be limited to the first month following launch, many players are questioning this decision and wouldn't like to see layering in the game at all.
For another example of lighting, we looked at Elwynn Forest. We had a period in Warcraft’s history where we changed all the lighting equations and as a result, our environment artists had to take a pass over all of the zones to improve the lighting and take advantage of the new equations. To recreate the original experience, we had to rewind those changes. The first thing we did was restore the old lighting data. This brought us much closer to the original lighting—and with a few more changes to the distance formula, fog formulas, and some changes to shadows, we were able to bring things even closer to the original lighting.