Hack & Slash is any sort of Action-Adventure game, or Dungeon Crawler where the bulk of the game is based one exploration and loot gathering.
Typically these games consist of two attack buttons, with a handful of combo's that you repeat over and over throughout the game.
Compared to the combat in those games, TH is quite alot more fun. That's not too say it's excellent, or doesn't have big flaws, as you point out the lack of visceral feedback as you hit enemies is a big problem, the sometimes jerky animations aren't the best too look at, and certainly if you are going to compare it to a pure Action title like DMC, GoW or Ninja Gaiden it's not even close to the quality of those games.
But at the same time, those games are Linear with a capital "L". They do not offer any sort of meaningful exploration, and in most cases the story is crap. I happen to really like the storytelling in Too Human, you may disagree, but the point is Too Human has things it does better than those games, athough combat is not one of them.
I agree the SkillTree seems a little weak, and I'm pretty dissapointed with the aspect of the "Human" vs "Tech" sides of the tree. It's supposed to be the heart of the story, i.e. Do you become more powerful by relinquishing your humanity, yet I couldn't even tell which side was which.
As far as getting the hang of the combat, there is almost no difficulty in the demo, it's extremely easy. So you can play through it, and feel as though you fully understand the combat due to the fact you are dispatching the enemies without much trouble. But, it certainly does become funner, more fluid and more natural the more you play it, and by my 3rd playthrough the difference was night and day.
I dunno, to each their own. I love diablo type games when the loot gathering aspect is done right, I really enjoy norse mythology, and the combat is more than passable for this type of game, so for me I'm looking forward to this. Probably won't buy it, but it definately deserves a rental.