I don't want people to get me wrong here. I really like the game, I just think some of the most important parts fail quite hard, but that is my opinion. I'm all for new paradigms in the RPG space, but really Witcher lacks a lot of customisation options generally typical of RPG. It is RPG-lite.
There is some compromise involved. The game is based on a series of fantasy novels. The characters are well defined, fleshed out, and the story and how the plot unfolds are dependent on the hero's characteristics. In turn, players are asked to surrender their ability to customize things such as appearance, classes, deities, and race. Keep in mind though, there are still many "customization" you can make, e.g. choices and consequences (plot progression, big one), skill development, equipment, etc - these are the less superficial customizations. I think this is a good compromise given that we get a great and tightly-knitted story in exchange, which is not possible if you can have the degree of customization seen in the likes of some other RPGs.
As for hack and slash spamming, the previous reply to me was of course correct. I don't do that on bosses but I do that on everything else. In most cases I don't even pop any abilities. I'm just really good at spamming my space bar! Enemies telegraph their attacks so there's a good deal of time to react and it is quite easy to figure out that groups are trying to encircle you. rolling around is simply very effective at countering the masses of mobs in the game. by in large, the game can be circumvented by rolling around and striking quickly. It's not an exploit, just the way it was designed. It's uber cheesy but I'd rather use that than a defensive system that may or may not work.
I do spam the spacebar a lot. Mix that in with potions, cast the occasional Yrden or AoE Aard, and leap attack a far away enemy with LMB, RMB when in range, and put obstacles between me and the mob, wait until the enemy finishes their combo and strike while he is recovering, incite inter-faction fighting (often which the drowners emerge victorious - puns intended). It probably is just me, but I don't really find the whole combat system to be a spam fest.
To respond to your other points, block/parry not as useful when un-upgraded, esp. when you can only block the enemy where you're aiming at. Interacting via mouse. But blocking an attack staggers your opponent giving you a free hit, sometimes easier than rolling at the back and sneak attack. Riposte is even better.
For looting/interacting, it is sometimes a pain in the ass. But walking (holding down shift) instead of running mitigates the problem a lot. You can press "Space" to loot all. Mouse is software-emulated hence the sluggishness (not overly) but I (and many others) got used to it. It is still somewhat sluggish even if your PC can perfectly handle the graphics.
While there are some parts/bugs that I don't like, I don't agree with descriptions such as "Clickfest", "100% consoled", "extremely limited RPG", "the combat is one unmitigated disaster", "The mechanics fail. The UI fails and the combat fails".
But heck I might be wrong. *Maybe* fast-paced, twitch-based, action-oriented games belong to the territory of consoles after all, and bringing such games to PC is blasphemy