Gothic 1 and Gothic 2 were great for their time. Gothic3 was already dissapointing to me (but still "ok"), 4 is rather boring.
The third game was actually the one that was most similar to the Elder Scrolls though. It offered the most free-form exploration and player choice out of any of the games in the series. It's actually my favourite Gothic game on those grounds alone. I think the biggest problem with the Gothic games is the crude combat system, which both Risen and Arcania inherited. Hopefully they'll have stripped it out entirely for the new Risen 2 game, and build a new system in its place.
Of note to anyone that's interested: Gothic 3 has had significant patching both from the developers and the modding community, and even some high-rez texture packs lately. Most of the old bugs are squashed and it's actually pretty good now.
The crude combat system remains though. <_<