Gothic 3 is divisive. There are some people who say that after the Community Patches, Quest Pack and Content Mod (don't know if the last two are available in English) it's a decent enough game, some say the whole game mechanics are so utterly broken that nothing can save it (it definitely has a horrible fighting system that can never be fixed).
But of course, there are some people who love it, and I even know of a guy who thinks G3 is the best Gothic.
There is also the
Community Story Project. That attempts to do to the story what the Community Patches did for the tech - add chapters, a deeper story with more quests and dialogues (no dubbing obviously) a changing world, a faction system etc.
But it won't be released anytime soon, and an English translation will probably take even more time.
Forsaken Gods wasn't developed by Piranha Bytes, but by an Indian team that probably never played a Gothic game in their life, and was just created as a transition for Arcania, which was also not very well received. PB themselves said they only count their own games as canon.
The first release was completely and utterly broken, but there is also a Community Patch for Forsaken Gods, but it also only fixes the technical side of things, and leaves the content untouched.
Also keep in mind that Gothic 3 is still very hardware hungry, because the Piranhas were never very good at optimizing their engines, but also because it can't use multiple cores, which means you need either a single-core CPU (which I doubt), or a multi-core CPU where every core is very powerful. But if you can run Gothic 3, Forsaken Gods shouldn't be a problem, it's pretty much the same game.
In my opinion, if you want more Gothic, you should be better off playing mods.
Sadly not all of them are available in English but I tried to find some of the better ones:
Diccuric (for Gothic I) was pretty much the first mod that was a complete conversion and had a larger scale. It has it's own world and story and is still regarded as one of the best mods. The modification is only the first part, and it was intended to become a complete stand-alone game, but I don't know if that's still going to happen.
Dark Mysteries is a Polish
(website here) mod that acts as an add-on for Gothic I. Haven't played it myself, but as long as "Welt der Verurteilten" isn't available in English, that's probably the best way to expand Gothic I.
Velaya (for Gothic II) is pretty much my favorite modification ever. It tells the story of the Gomez' babe after the barrier fell, has extremely good and funny writing and is very imaginative, without being reliant on new features like many other mods.
The German version even had extraordinary voice acting, partly done by professionals.
There are of course others, probably even some in original English I don't even know, but your best bet at discovering those is - as always -
World of Gothic So, those are all free and I think they will offer you more value than Gothic 3. ;)