This question goes out to all Gothic and Risen die hard fans!

I did not play the original Gothic 1+2, only Gothic 3.

Now since everybody says the Risen games come closer to the original Gothic series than Gothic 3+4 I want to know if it is possible for me to enjoy the original Gothics someday when I now play Risen before? Or will it be so similar that I might think the games are a letdown because I played the technically more polished Risen before?

No.

I don't think so, anyway.

If you liked Risen, Gothic 1 and Gothic 2 are very similar mechanically. They're older so the graphics aren't as nice, but the story and atmosphere are better than Risen.

Risen functions very similarly to Gothic 1, if memory serves. If you liked Risen you should also like Gothic.

I'm not a die-hard fan, haven't played Gothic 3, only 1, 2 and Risen 1. as already stated, the games are pretty similar. Risen has - of course - better graphics, a bit more diversified skill system (although still very flat), Gothic 1 has the great story idea with the magical barrier, Gothic 2 offers the best package overall. For me Risen is the weakest part compared to the older Gothics.

Gameplay-wise the Gothic and Risen games are very similar. If you know one of them and you like it, you'll very likely also enjoy the other games and feel very familiar from the start.

I personally started with Risen 1 as well and played Gothic 2 and 3 later. Except for a slight letdown because of the outdated graphics in Gothic 2, I thoroughly enjoy all parts and have finished them at least twice each. They are simply wonderful games.

If you liked the initial Risen feel that you are the weakest one of the land and you have to work hard even to kill a little wolf, while in the end of the game you are quite a superhero, I think you will like G1&2!
I played first (I think when they where released!) Gothic 1 and 2 and enjoyed it both, even if I weren't able to complete G2; recently I played again G1 then G2 then G3 and then Risen 1 and enjoyed all of them! For the graphic, both G1 & G2 has textures packs and mods that significantly increase the graphic (of course it'll not become a next gen one!), by the way I agree: they are simply wonderful games!