Single braid are indeed very easy. At some point, you can do them in your sleep, well, almost. The site L-36.com has a number of detailed instructions how to use Amsteel rope in particular for various projects involving splices.
Double braid is a bit more involved, but, with the right instructions, it should not take hours. I find that I need to refer to the instructions every time - it's really hard to remember them. One thing that's really useful (if you mainly work in the same diameter rope) is to convert all the "fid length" based measurements once and for all into inches and write them down on your instruction sheet.
For instructions I like those published by the Sampson ropes company. You can google and find them online. I splurged and bought them as a wirebound little booklet from a local marine store some time ago.
Twice I've had splicing instructions fail me. Both involved single braid ropes, and both times, the issue was that the rope wouldn't open wide enough to accept a bury for the tail. In one case I was splicing double braid to single braid and ended up having to splice in a short length of larger diameter single braid, to make the splice possible at all. In the other case (single to single) I just had to give up. The rope had been used a few times (not hard enough to matter, I would have thought) but the braid simply couldn't be opened wide enough to accept a tail of the same rope. In both cases, it's entirely possible that the opening for the next size up of the same rope would perhaps be a little wider than what you'd expect purely on a scaled-up basis. Just a thought - don't know enough about ropes, but note that many instructions use "examples" of ropes that are larger diameter than what we need on the DS, especially for the new high-strength materials.
Before I tried splicing double braid for the first time (I was a bit intimidated by the instructions then) I needed several eye splices for a system of pulley's in my garage. I did those with thimbles and by laying the working end along the standing end and wrapping both with wire. Totally unorthodox, I know, but the wire dug into the rope deep enough to prevent the two parts from slipping and I had the full weight of a DS across two of these "splices" - and they held.
So, there's a lot of scope out there for "ugly" solutions.