TL;DR
- open offices might increase the frequency you bump into people and thus interaction, but that was never a real issue in the first place.

- open offices are less productive as a whole due to the increased noise levels and the increased number of coffee machine talks all over the working floor.

- privacy is gone. On the plus side this is forcing people to work. On the downside this also reduces job satisfaction for many.

- one large room makes you no longer be able to regulate temperature, lights, and that sort of stuff. Less control on your environment. Some people like hot rooms, others like fresh air in winter.

From what I observed open offices sure can be fun. A bit too much even. Usually you meet people at the coffee machine if you weren't directly walking up to them. You usually spend a coffee for some smalltalk, just because it's fun and you were walking around anyway to clear your mind. In an open office it's like fulltime coffee time. There are always people having fun stories from past weekend, last holiday, or just beer time. Sure you know a few and pop in more frequently than you would have in coffee machine talks at the coffee machine. This is not a downside for you personally, you might perceive it as fun, but it kills your output.

A lot of reactions in favor of open offices mention it's ability to quickly get a hold of someone. I never understand why the ability to quickly ask colleagues anything is a pro for open offices. I have worked in both and to be honest there is no difference in time it takes to reach out to a colleague. If they are in my room, the people you typically need most, it's the same as an open office. If they aren't, it's one walk away. The distance doesn't chance that much. Get out of your chair, visit coffee machine on the way, and walk into the room of the person you need. Pros might want to check the chat status, if green he's at his desk.

I'd say if you think you need to schedule a meeting for every question there is something else wrong, an open office is not going to help you there. Also, if you need a meeting now you will need it in the open office as well. Only on paper these two environments have different protocols when it comes to human interaction.

Noisy. Well, enough is said about this. I don't mind too much but others do.

Control on your environment is something I really missed. Everything is set to general population. The heating is average but I really like fresh air even in winter. The great perk of a company for me is always to have a heater and open the window ( :) ). There are plenty who like warmer rooms though and after a couple of months, or years, you learn to not take the same room. No offense but either party agrees on the different preferences. Same holds for light. Some people close all sun screens the moment the sun peeks in. I personally like the sun and only close stuff when it's directly on my screen. With large rooms it's always in someone's screen and the sun screens are always down. I have had a summer where basically they were down all day.

I think ideally you need a mix. I'd say the only thing in favor of open offices is the increased interaction. If you accept less productivity in favor of potential great ideas spawned in that one case where two people bumped into each other at the right time than by all means make it happen. Doesn't need to be an open office though, can also be open spaces where you create an incentive for people to hang around more frequently. Relaxing areas. Make sure you communicate it's okay to be there as well. The rest is basically against open offices. Personally I don't think they are worth it for engineering departments.