Witcher 1 Combat

[MysticSlayer]

1. Does combat evolve beyond monotonously clicking on the enemy in time with the mouse thing, occasionally changing stance to suit the type of enemy you're facing?

Depends mostly on difficulty. Signs and potions will mix things up, but at least on the lower difficulties, they aren't necessary in most fights. Some of the later fights do require you to consider your position in relation to all the enemies, as simply running in with group style won't always get you out alive. For the most part, though, the actual swordplay stays the same throughout.

2. If combat does remain this boring, would you say that the story and world of the first one make up for it? I mean, Mass Effect 1's combat was arse as well, but the lore and characters gave me enough motivation to slog through it at least twice.

For what each of them do, I would say that The Witcher and Mass Effect are on the same level in terms of world and story. Just don't expect The Witcher to be Mass Effect, as it works on a much smaller scale.

3. Would the latter games be at all playable/comprehensible if I skipped straight to Witcher 2 or 3?

I can't say anything for The Witcher 3, but you should be able to make it through The Witcher 2 without much trouble. Just don't expect the gameplay to improve that much. I would even say the first game was better. The first game had at least some appeal with needing to understand what weapon, stance, signs, and potions to use, and it served its purpose of complementing the world. The second game was just awful with practically no redeeming factor, especially if you've played plenty of action games.

But The Witcher has never really been about the gameplay. It is about the world and story, and if you can focus on that, then you should be good. Considering you said that you were able to slog through Mass Effect's gameplay for how great the world and story are, I would say that it shouldn't be too hard for you to enjoy The Witcher games.