The major changes I noticed between the two editions are as follows:
Limits prevent characters from being overly min-maxed. Each of them is centered around an attribute that is typically dumped in normal characters; the most important attribute for the physical limit, for instance, is Strength, though other attributes weigh in they have the same impact as Strength does alone. This means that you can't build a "never gonna fight close quarters" build and just dump strength and expect to do well in other physical areas, encouraging a well-rounded thing.
Mystic adepts get a huge buff. I'm not exactly sure that this is a bad thing; they still can't astrally project, but they get the powers of both mages (other than astral) and phys-ads pretty nicely. Were they still using the BP system, this would be a flaw, and I'm not sure about allowing them as the third pick on your priority system, but I think the reason that people are upset is because they don't astrally project as much as they should when not a mystic adept.
The priority system really makes things a lot better. It prevents some of the worst cheesing during character creation (don't get me wrong-it's still possible, but you have to know what you're doing and make some sacrifices).
Combat's been changed rather heavily on the bookkeeping, but not so much the execution. The Accuracy limit keeps pistols from killing Great Dragons, which is a nice touch, but also discourages just dumping into the newly increased skills and maxing them out right away. It also makes smartlinks a more tangible advantage, as do laser sights. Armor is now a single rating for stun and physical, which makes it a lot easier for new players to understand, and, in my opinion, more realistic.
Hacking's a lot better. Mind you; the wireless thing contains some logic holes and gimmicks with the new benefits it gives stuff like cyberware or laser sights, but hackers can enjoy a target rich playground with new rules for hacking that make prepping a hacker 90% easier and playing one about 50% easier; GM'ing hacking also became a lot easier. In addition, some of the more broken technomancer stuff has been revised so you now have a reason to play a decker instead of a technomancer every single time.
All in all, it's faster and more streamlined. If you want my "reviewer" version, you can check it out on my blog, but I've said pretty much everything I said there here, only without the sales pitches.
Evo share holder Hideo Yoshida may be an obsidiman.
No t'skrangs have been reported in the Sixth World (Shadowrun).
I've found this wikia site rather reliable so far - but, of course, I might be wrong, and other answers may provide more up to date and more precise information.
Essence can be recovered, but it's very difficult. By default, removing cyberware leaves an Essence "hole", into which new cyberware can be installed. In 3rd Edition, Man & Machine handled several different ways for Essence costs to be modified via surgery and the like, and things like delta grade cyberware can decrease Essence costs, as can certain qualities, but it's not possible to regain Essence by itself.
Until 4th Edition's Augmentation came out, at least. It's technically not SR5, but it's part of 4e which is pretty similar, and better yet it's some of the parts that don't have mechanical changes between editions.
So, in short, yes, it is possible to restore Essence loss after removing the implant, but it's difficult and expensive, not to mention time consuming (.1 Essence a month, and 20k per month, plus a hefty start-up fee). That said, it might be more readily available in 5th Edition.
In addition, I wouldn't be entirely unsurprised to see a metamagic for this at some point, especially since it's the sort of thing that I associate with Shadowrun's metaphysics (more from Adepts on the Earthdawn side) advancing to a certain point.