I honestly doubt Zoe's voice change was for artistic reasons. They do have most the original cast. I think we can all agree while being reasonable that there was no guarantee everyone could, would reprise their roles in this game. Most of the original cast has though.
This game has updated graphics. In the early 90s we had old school adventure games , they were pixelated. Mid 90s that all changed. Around 97, we saw this with Curse of monkey island, the graphics were so dramatically different. The characters were different in CMI because the of the art style of the game. It had to be consistent. They changed it again when they made EMI which funny enough occurred during a transition of gaming where CGI was just getting huge in the year 2000. Most adventure games didn't survive CGI, they tried it and it was terrible. Simon the Sorcerer 3D comes to mind. Not a terrible game, it's all right. So fans of the adventure game genre have learned that it's natural to see updated graphics in a game. Also that characters change. The only difference there is that it was an animation game and that characters could be animated, drawn differently. These games are some what more realistic. Ultimately the characters in these games are only life like, not real life examples of people. People still argue about character design from Monkey Island today. Then there was Tales of Monkey Island, which updated old CGI graphics, much like they tried to with Chapters. For tales I think they tried to blend the Monkey Island two and 3 Guybrush.
They only have one character to base their remodel off of for Zoe, and they wanted her to look more realistic. I can understand how challenging this might be and how everyone might not at first be comfortable with the result.
Though it's actually pretty common for this sort of thing to happen.
What you're experiencing is normal, especially after such a long wait. This game has take forever to be made. With the case of TTG's they had a small budget, and they made episodic adventures so they made smaller sets often and the graphics were so so and ... But I really like what they did with Tales of Monkey Island.
New voices as much as you hate it, they can grow on you. I remember playing Still Life two and at first I just couldn't get used to the new voice. I did hate the change, it just didn't feel like the same character, and she had this stupid red dress on the whole time. It was like if April Ryan in the second game wore a dress. But after a while I accepted it and it was fine. Some times maybe even a better performance than the original actress. I LOVED the first game. It's a masterpiece. The character reminds me of April Ryan, which is completely intentional.
I highly doubt that Ragnar and his team are over looking her talent or settling for less. I'm sure that they realize it's not exactly the same voice, but that she is a valid candidate for the job and will give us an emotional experience. As hard as it is to accept at first change in video game series is a very natural thing honestly. You might hate it at first but it might grow on you. There are alot of changes to series like Monkey Island.
By the way Still Life was some what inspired by April Ryan, just an interesting fact. I won't lie and say that change always helps a game. People loved CMI because it came at the correct time. Escape from MI had the same problems most adventure games had trying to use CGI and new interfaces at that time...but it still wasn't rated that critically. I won't say that all changes pan out in the end, or that everyone is comfortable with them, but a game can still be very entertaining and excellent regardless of changes.
It's very common in video game series to change like this. Didn't they do similar things to the Mass Effect series? Maybe I'm wrong.
Anyways, I'm sure it's going to be alright. I sympathize of course. Having most the original cast there Zoe will be missed. I'm thrilled they got Sarah Hamilton to return. I understand how you feel entirely, because every gamer who has played long enduring series at one point or another is susceptible to experiencing this. As un natural as it seems, and as much bickering as it is going to cause, it's actually fairly common.
It's worth noting that April Ryan has ALREADY changed from the first game to the second, so it's not a real surprise that 10 or so years later that Zoe and April Ryan may change again. I understand your frustrations though. At first it's a shock and you want to hate the game but you may end up enjoying it quite a bit and appreciating the performance the actress gives. I'm sure she'll try her best.