I was very excited to try this game; i joined; was lucky enough to be last... so i waited 10 minutes to actually do anything.
Also I didn't understand a thing from what others where doing so the first impression was terrible.

Please either put a setable time limit on player turns or allow players to make actions in parallel as long as they don't affect eachother.

I'm not sure adding a time limit is the way to do it. Some turns are over in a minute, while others takes more time. I do agree however. Being able to do something while waiting for your turn would be neat. Looking through your inventory, cards and such.

Maybe it would help if each player can access his or her won character sheet while it's another players turn. This way, one could go through newly acquired cards, or the quest and lay out a strategy for the next turn.

But in general, I thinks this will stay an issue. Why?

This game emulates a classic board game. Most fun in board games derives from player-interaction. 70% verbal, 30% game mechanics.

You could improve the game by adding mnore interactive game mechanics, e.g. how can I hinder another player to complete his or her quest. is there a possibility to trade items. can I aid another player in his or her quest and gain something from it for myself?

and hey, how about some basic, lasting character developement?

First of all, I was not able to start a multiplayer game. I could join lobby (with 2-5 people), click "start", but after 5 minutes of waiting nothing was happening.

Speaking about being able to do something during other player's turn, I'd suggest to look at iOS version of "Lords of Waterdeep". For me it is one of most polished digital board games atm. You can look through everything during other player's turn.

I noticed the game was quite slow as well. I feel like it is because there are buttons players must click but there is only 1 choice. Or there are choices like pick 1 of 3 face down cards. So people take like 20 seconds deciding, when all the cards are random. It does not matter which card you pick! Or rolling dice. So yea there are a lot of points in the game where you are given choices where there is 1 choice and it just adds up.

Oh yea and also when it is not your turn, or even when it is your turn you are focused into this one thing. Like when you pick your quest, you can't check what your investigation to proof ratios are. Or other things about you, so they give you choices were there are none and they take away information where you need it the most.

agreed. the game feels slow. also new players kind of take quite long for each and every turn.

it would be nice to either - as already said - be able to view your own cards, character sheet and stuff during other people's turns OR/AND see every move exactly the way the other played did it.

Here's an example for those who play Hearthstone:
In Hearthstone your opponent is able to see every move you make, animations show which card he's currently looking at and so on and so forth.

for Witcher Adventure I'd like something similar, maybe even seeing mouse movement of the one who's turn it is. that way an experienced played would notice when someone is stuck or has a hard time deciding. Via chat (and please include voice chat in a later build) the experienced player could then offer help.

it would be a nice feature IF you also could access all your own stats, cards and stuff - as already has been said too - to read thoroughly through texts and quests and plan ahead.