My problem with the Magic tree is that you have to upgrade several different signs on the way to the top. In terms of combat that seems like it'd be clumsy because you have to keep using the CTRL menu to pick a different sign. Also, if the combat progresses as it did in the first game, I really would only focus on a couple of signs in the first place.
The Alchemy tree just seems like it would be really expensive in combat. All those oils, traps, and potions are definitely going to add up, and I'm not sure how effective it would be overall.
On the other hand, your swords are going to get a lot of use, and it seems to be the primary combat skill. Being able to counter attack seems to be extremely important based on the early fighting, at least.
It definitely seems like the trees are designed to encourage specialization, since all three trees have heavy +vitality talents near the top. I guess it depends on how many total levels/talent points you will get during the game, but I really see no reason against getting most of the sword talents first.