I got one of these today; although I submitted it, it certainly didn't give me the opportunity to express my view on the content to any degree of detail. I haven't engaged the Galactic Command system yet due to a lack of interest after the initial first day of hype. Other than that, here was my view on changes I was most interested in, in regards to the current state of the game, post expansion.
TLDR: Though the Cartel Market releases great content, the attention it's given detracts from the gameplay value of "earning" your character progression. And since it's unlikely there will ever be even new advanced classes (e.g. no need to create new class story), I think it's important for continued replay value for advanced classes to be given new abilities to diversify their kits, and improve the power fantasy of each class/talent build.
My primary concerns with the progression of the game are twofold. The first centers around my perceived imbalance of the Cartel Market system. I love the items released through the system, and have personally invested a huge amount fiscally to obtain Cartel Market items. However, I feel the effort that goes into new Cartel Market releases greatly detracts from the gameplay potential. There are so few ways to obtain stimulating rewards with diverse visuals through gameplay, whereas the Cartel Market churns out high quality items in every field (armor, weapons, mounts, toys) on a constant basis. There's nothing wrong in my opinion with micro-transactions, but it is balanced in a way that makes me feel I'm just buying my character's individuality, not that I'm really earning anything towards it through gameplay. It hasn't stopped me from enjoying the game overall, but it has definitely diminished my excitement to play new content, and to invest more time overall in the game.
Secondly, and tied to diminished excitement to play new content, would be a complete lack of dynamic class changes since the game has been released. I've been playing since the game first launched, and each class plays essentially the same as it did from the start. There have been the addition of a few new abilities to each class, certainly, and tweaks to existing abilities, but they haven't, in essence, changed the "feeling" of any given class or talent rotation. Every class still feels the same to play, and has had nothing new to chew on and get excited about to add to their character fantasy. To make a comparison, in the new Legion expansion of World of Warcraft, the Artifact weapons that were introduced each added a new Artifact active ability for their respective Talent tree. These were wonderful additions to the power fantasy of the respective Talent builds and to the overall character fantasy of the classes. By comparison, the new release of Knights of the Eternal Throne simply tweaked several existing abilities, added new ones only to certain advanced classes, and stripped a great deal of shared abilities with the attempted idea of separating the play styles of each advanced class. This wasn't exciting at all when I first logged in to the expansion. I had nothing new to try out, nothing new to play with, my class, in essence, was playing exactly the same as it had beforehand. Class changes, in my opinion, add an enormous amount of replay value to an on-going game, as they force players to re-evaluate their play style, and learn more about their character as they do so, testing their new abilities in different scenarios.