My experience on 0.4 so far.

So I played the new sorc ascendancy to the end game and here is my feedback of the league so far.

The league mechanic itself has a very good base. But there is lots of issues and it feels to be put together
in a rush. The room upgrading feels like it is purely RNG. There should be a clear way to upgrade the rooms.

In Vaal temple, there are plenty of crafting benches but in end game hardly any.
This is really weird, but then again in end game you should have currency to do your crafts.

Getting finally to the Architect and Atziri, beat them and close the temple to find out that you have to
rebuild the whole thing. (Haven't played after the temple patch but will do it after a little break.)
This feels so bad, you spend hours running maps to get access and building your temple, click aaaaand it's gone.

There is a limit of 12 stones on one run so basically you can do 12 maps, clear the Vaal thingies and then do 2
temple runs. In my opinion this should be raised so we can gather up temple runs when we are doing mapping.
this would be nice since you could map for the Vall stones and then focus running the temples.

The mapping feels so boring thought. I found my self just running to the boss and killing it, I don't feel
like clearing whole map would give me anything extra since I just wanted to progress my atlas.
I was hoping that the temple would cover some of the end game patch we didn't receive but it being limited to 2 runs at a time, nope.
We will see what 0.5 brings to the end game.

The new sorc ascendancy was great, good enough clear and good single target damage so it was smooth. The must be a bug in the passive tree,
when you check changes to skills when you hover over Minion Damage nodes, it shows that there is no changes. You check the tooltip, no changes, go into map changes.
But all together it felt nice. I had a build where I had only frost bomb as character damage to give exposure and to use Ruzhan to give more exposure and then used Djinn skills with spectres and ice and storm mages.

TLDR: There is a good base in the Vaal temple league mechanic, it needs some changes and care but the idea is awesome. End game is meh, have to wait until 0.5.
New sorc is fun and have to say that I was having a blast with it even when it was my first ever character I built myself to fit my playstyle.

I will be having a small break and see what will be patched. Need to touch some grass before the snow arrives.