First, congratulations on you fist smoked sausage.
I have to be honest and tell you, that the recipe you have selected for your first attempt is not easy.
You need to gain some experience, so to my opinion you should go with small steps.
There are may factors which may impact both taste and texture of you product, so let me mention just a few , which are absolute basic.
1. Meat quality
2. Curing
3. Preparation
4. Smoking
5. Hot processing
6. Cooling
So as you see, there is a possibility to do an error on each step
Don`t worry, just for your next try select something easier. OK enough "smart ass" talking, moving on:
I think that you did not dry the sausage before you started treat it with smoke, this is very important step.
What I mean by dry is that the sausage ( and all other meats ) need to be dry to the touch.
Any moisture on the surface works "glue like" for the unwanted smoke particles. When this happens, the meat or sausage can be a bit bitter, or very strong tasting.
Another reason temperature. I see on the photo, that the inside of the sausage is less colored then outside.
You may need to hang a little computer fan inside your smoker to force smoke and temperature circulation.
Keep it running for all smoking process, from very beginning when you load the smoker, just switch the hot plate on and let it run for 40 min, then check if sausage is dry.
If yes, start smoking with smoke, if not keep on drying. Finally, why you dont use your Weber 18" WSM for soking?
Well, later on I`ll translate for you recipe for "Farmers sausage" which I hope will compensate you disappointment.