Welcome to RPGWatch!
First of all you should check GOG immediately. They are in the encore to their summer sale, with probably only hours left. Witcher, Risen and Gothic are on sale there, as well as many other RPGs.
In terms character development the Gothic style games are indeed very rewarding. Especially the older games. A good entry point would be the first Risen. It is basically Gothic 2, with a bit less depth but a completely harmless interface. If you like how it feels, go back to the old Gothics.
Gothic 1 delivers the best sense of accomplishment, IMHO, due to its simple and clean mechanics. You can literally "feel" how much your character improves by +5 STR and slightly better weapon.
G2 Gold is an all-time classic. Brilliant world design, good character development, interesting NPCs, high difficulty. Both games have the same ca. 15 minute learning wall. The interface itself is remarkably efficient, just not intuitiv.
The later Risens are more mainstream. According to the hivemind R3 is better than R2.
The star in Gothic 3 is the world design. This world is absolutely gigantic and still one of the most beautiful out there. The game itself is a gamble though, even with the community patch. Hit or miss.
I'm not a Wizardry fan, because you can't make more than 3 steps without running into another group of enemies. If you want to try the series, GOG has Wiz8 for 1.89€. Or wait for the BundleStars pack to come back. Could take a bit though, because you're a week late.