First off, if I had actually played G3 through a few months back, I would not have mustered up the courage to start another round with 1.7. A few *years* back, for sure, but only a few months, no way. I'm a fan, but not *that* big a fan -- this is one huge game, as you know, and a massive time sink, and especially the early game of exploring Myrtana, running Fedex quests for XP, and building up your basic survival skills takes a long time and is really very much the same no matter what choices you make or character you build.
Anyway, I played 1.6 a fairly long way in, past the early game, to the point where I had done most of the non-liberation quests in Myrtana and was starting to explore Nordmar. I started over with 1.7. It was worth it, but only barely -- I'm sort of ticking things off a list rather than really enjoying it; what keeps me going is the knowledge that I'll soon confront the mid-game without being a combat god.
So much for the preliminaries. What do I like? Well, I'm playing with Alternative Balancing on, and am making a mage build, and this time around it finally feels like Gothic -- the game will poke you in the eye big-time if you wander off into areas where you shouldn't be too early on, and the feeling of progression and achievement that comes with growing your character is that much bigger. I can't win the tougher arena fights anymore without first building up some melee skills; goblins will turn me into shishkebab if I barge into a mob of them; shadowbeasts are *scary.* That sort of thing.
The alternative combat AI is a big improvement. It's dynamic and responsive, and click-spamming (mostly) doesn't work anymore. You have to be much more careful about timing, about picking off enemies one by one, and about using combined tactics -- e.g. weakening the mob first with fireballs and/or archery, then finishing them off with melee. This doesn't turn it into The Witcher or Jade Empire, mind, but it makes what used to be a silly chore into a perfectly serviceable gameplay element.
I also like the rebalancing that's been done for the mage build. The skill trees make more sense; while the basic mage skills are cheap enough (i.e., you can still spice up your swordsman or archer with some magic), the real "mage specialization" stuff is expensive: once you've made the decision to go for Mana Regeneration, there's really no going back. Conversely, staff fighting has a lot more oomph; you're clearly still behind any sword specialist of a comparable level, but not so much behind you have to run screaming at the first sign of toe-to-toe combat. I'm coping fine against weaker enemies with my blade staff, and the tougher ones go down with it after being softened up with a fireball or two first.
What hasn't changed is the best thing about 1.6: it just *works.* Performance is all-around excellent; there are still some stutters, but not so much it really makes things unpleasant, I haven't had a single crash or encountered a single bug that goes beyond cosmetic issues such as a cohort wading through part of a cave wall.
All in all, I'm hugely impressed with 1.7 -- it takes Gothic 3 back to its roots, as a brutal, hardcore action RPG focused on exploration, with gradual but enormously rewarding character progression, and real-time combat that's basically dead simple, but requires just enough tactics that it isn't incredibly tedious. If the game had come out in this state, Gothic fans would have been ecstatic.
My recommendation? Give it a rest for a few more months, and when you're good and ready, itching to give Myrtana another visit, then give it a go. If you've just completed the game, you won't get enough fresh, new experiences to stop it from feeling like a grind. If you're really curious, though, by all means give it a spin -- the new features are pretty obvious already by level 10, so it won't take you long to find out if you want to continue or not.
But do keep in mind that this is the old Gothic -- you won't be able to do many violent quests until you've built up your character a bit; if you try too early, you'll be staring at that excruciatingly slow red bar a lot. So don't.
(Oh, and -- without AB and alternative AI, forget it; that makes it the same ol' 1.6 with a lick of paint and a bit of polish on, improvements, for sure, but nothing to warrant a whole new play-through.)