McNett Gear Aid Seam Grip does a great job at keeping the water out BUT it sets up kind of tacky, which you may find annoying or maybe it wont bother you. I stitched up some slices a Montbell jacket with it and as long as my finger doesn't run across it, it's fine. That's just holding the sides together and putting it over the hole. But, I would recommend putting some tape on the outside, making sure to line up either sides of the rip, and seal it from the inside. It will be almost unrecognizable. Pick a tube up at REI or somewhere similar.
I also had a bad run in with a tree on an AK jacket it have and it slit the arm. Because it is down insulated and it only tore through the top layer I couldn't get to the back of the seam very easily. Looking for another solution I found a clear patch kit from a brand called Tear-Aid. As long as the fabric is super clean and flat before you attach the patch, it should do just great. The Tear-Aid stuff is super cheap too. I bought mine at Sportsman's Warehouse.
Either way, you get a pretty inconspicuous fix without resorting to a goretex patch of a color that doesn't match. If you have it professionally repaired it's gonna cost you close to the cost of a new jacket, which I think is ridiculous.
As a side note, don't use duct tape. The adhesive compound used in the tape will just ruin your jacket and fall off when it gets wet.
Good luck man. You'll figure it out. PM me if you want pictures of the individual repairs.