I've run through both Imp and Republic storylines for Makeb, plus the staged weekly which is like an epilogue to the story in mission form. I really like it. Each side has a different reason for being there and each side comes out different on the back end. I *loved* the final conversation on the Pub side because it really highlights how the "Open Hand" policy they have can bite them in the ass. Still getting a handle on the gameplay changes overall but from a 'Sin standpoint I can't complain one bit. Deception is now God Mode in the right hands and against people who don't know what they're doing. Darkness got a bit of a boost, especially in PvP since they made Shielding capable of affecting Tech and Force abilities plus having it work through Guard. I've never done Madness and I think people are bitching about that spec but it was always a poorer version of the Sorc stuff so I'm not sure what they can do there. Oh, and before I forget, the Shroud line of quests are fucking awesome. Those by itself are worth the price of admission.
There's a decent amount of stuff to do but in the end it goes back to things like Dailies, Flashpoints, and Operations. I like the idea of the Staged Weekly but some of the missions are annoyingly long (which I guess is why it's a weekly). The GSI stuff is a nice change of pace but it's a mixed bag. Doing the dailies for those in any place but Makeb seems like a waste of time since you can do Makeb dailies and those at the same time. The Seeker Droid stuff is SWTOR's version of Archaeology, complete with the usual randomness but there's less running for it since the locations are static.
There's some issues so it's not all sunshine and roses. Many of the Achievements are messed up. I think they took a step backward with regards to abilities firing off. I have queued-ability set to .75 and sometimes I just have something not go off even after pressing the button multiple times. Crew Skills are kind of messed up right now with some of the missions returning just flat out the wrong item. Mat requirements are kind of ludicrous for some stuff and not at all in line with what's come before.
Overall it's a good addition to the game. Not worth $20 for non-subs, just because it doesn't feel like $20 worth of content. Maybe $15. For subs, it's definitely worth the $10. Also keep in mind that expansions aren't just their release, not in MMOs. So it'll be interesting to see where things go from here because I've not seen any news in regards to what they plan to do next.
On a personal note, I'm hating the usual post-expansion gauntlet of having to gear out again. That said, what I do have allows me to run with just shy of 38k hit points in Warzones as a 'Sin Tank. Can't wait until I min/max. Gonna be a bitch though. I got my Slicer up to 450 like two days after early access started and since that time, running missions as often as I possibly can, I have 4 of the Purple Slicing mats needed for the Advanced augments. You need 4 for each one. The Prototype augments are still much better than the Advanced 22s and those are easy enough to get so I'll just run those for the time being. Oye.