So, my opinions, in rapid-fire form-
Mines are silly OP.
Mobula is engineering hell.
The new UI elements in the lobby area are nice.
I really don't like the extinguisher changes.
Mines are silly OP.
Some of the chat changes are good, some are not good.
Mines are silly OP, especially with Lochnagar.
It's fine that extinguishers received a nerf, since they really trivialize putting out fires, but they way they were nerfed makes the chem spray a necessity, and makes heatsink ammo a little too mandatory. You simply can't afford a 5 second repair cooldown in the middle of a fight to put out a small stack of flames. It's much better to pre-spray important components with chem spray so you don't have to deal with fire as often. An experienced crew will know to bring chem spray and heatsink ammo, and generally know how to deal with fires, so this change punishes new players far more severely.
As I mentioned earlier, I'd much rather see the extinguisher and repair cooldowns be separated, and the extinguish cooldown be transferred to the player's tool rather than be on the component. In other words, a player should be able to spray whenever, but only be able to spray again (whether it be on the same component or another) after a set amount of time. Justification could be that the extinguishing tool needs to build up pressure again.
The chat system looks nice, but I don't really like how global and match chat are separated (EDIT: they're separate tabs, so you can't see global chat and match chat at the same time). I get that you're kind of running out of buttons to choose which chat to type in, but this makes me think it might be better to switch over to something like what WoW uses. In other words, press Enter, type /p or /crew or whatever to choose which chat you want to type in, and remember which chat you last typed in when you hit enter so you may not need to type /[channel] again.
Also, in such a team-oriented game, you should not be able to close the chat window.
Mines are a trickier issue to tackle. They're simply too deadly. They're too easy to stack and they probably do way too much damage. I'm not sure how to fix them.
As for the Mobula, I haven't played on it enough to really get a feel for the ship, but I will say that it would be really nice if there were stairs or ladders leading up from the side engines to the area under the center engine. Components are just ridiculously spread apart, so please throw us a bone and make it easier to get all the engines in one go.