I am a notorious nitpicker, and my list of complaints against the Witcher is fairly short (I'd still give the game 4.5/5 stars) even if I sound whiny.
I'm not sure I get the fast travel options complaint? The maps (levels) are not that large, and you are usually confined to only one at a time. To me having some teleport gateway or whatever it is you have in mind on such a small map, in every map, would just look silly and break immersion. What exactly did you have in mind?
This is a pet peeve of mine (I used a ctrl-Y teleport cheat in Baldurs Gate II, saving hours of walking across maps), and the Witcher is by no means the worst offender in the gaming world. In general I sort of like Oblivions "fast-travel to already visited locations" principle.
One does spend a lot of time just running back and forth in the first four chaptes even though the maps arent that huge. You are right that teleports everywhere would be nonsensical, but I think see something like the kid that moves you around town in the Icewind Dale II prologue could be put into some of the locations. For instance it would be nice to be able to simply click on Alvin in Chapter four and say "let's go to the fields", "let's go to the beach" etc. Luckily C3 where you have to traverse the longest distances also offers a fasttravel service.
The principal solution I'd go for in an Aurora engine game would be to offer direct routes between all maps in a chapter where that make sense, but only make those available as you've manually cleared your way to the place once. An extra rowboat here, a guide there, etc... Or you could use the old method of Baldurs gate et al where you end up on the world map when you exit a map.
Your complaint about too many drowners to kill is definitely on target, but believe it or not you can easily fix this by purchasing a drowner repelling talisman in-game.
Sadly not a fix as implemented, for the reasons mentioned by others. Your memory of this being much less of a problem in the swamp than in the swamp cemetary (C5) is perfectly correct. In the C2-C3 swamp the monster density is low enough that you can run away from the critters most of the time even without the amulet.
The talisman would have been an elegant solution if implemented just a tiny bit better (make the drowners run a bit further away from the source of their fear) or if the engine had allowed you to exit areas or pick up ingredients with enemies around.
Btw, you can sheath the weapon, but that isnt a solution as it isnt the status of your weapon that determines whether you can leave an area or pick up things from the ground... This is a poor design decision that I think stems from the devs wanting to make it impossible to escape key fights.
As for the last point, that is just too much hand-holding and cuts down on replay factor tremendously, but that's just my opinion.
Not breaking quests in transitions is a design challenge of all event-driven games, and my first response is to implement the brute strength solution
I dont agree that "point of no return" warnings matter for replay value at all (the replay value of the Witcher is almost exclusively determined by the mutually exclusive, alternative quests and their outcomes, and having your NPCs state that you have to pack ALL your necessities in two or three more places wouldnt affect that at all), but I can admit that it could break immersion. The problem is that the game already warns you often enough to break immersion, but inconsistently.
You miss out on it in at least one crucial instance (the end of C1 where you might lose your potion stash and the sources of alcohol), while in another instance (the end of chapter 4) you may get such info shoved into your face by Dandelion when it isnt needed. Getting rid of warnings would work as well if some other aspects of the game were tweaked (the C1 situation would for instance be a non-issue with unlimited inventory), so I guess consistency either way would be an improvement.