Taking cover does not make a game "less hardcore". It can very well be as fun as the next game. Take the Uncharted series for example. Naughty Dog really knows how to mix motion-capture and live dialog along with seamless transitions from cutscene to gameplay without any problems. The incredibly realistic environments, which can even further be demonstrated in 2, use climbing and platforming mechanics mixed with cover-shooting action that immerses the player into the game.
Obviously, it's not an entirely realistic game, what with Drake climbing pillars and hinges through a [chameleon sting]ing -200 degree blizzard. But the point I'm trying to make is, taking cover adds a great sense of realism to a game. I use Uncharted as an example because it's the most true-to-realism shooter I know. I don't think a normal human being would run out in the middle of gunfire without getting capped a several dozen times. This is the realism Uncharted portrays. Taking cover, seeing where your enemies are, and planning who you are going to attack first. The latter becoming much more beneficial when you choose the "Crushing" difficulty setting. I can guarantee you right now, you will not make it out alive in the first Uncharted, if you just shoot whoever you want to shoot. The enemies are much more strategic and some even run right at you guns blazing, so you really have to know where and when to take action.
Believe it or not, there's (gasp!) strategy in taking cover, aiming properly and taking out first who would cause the most problems for you. I'll admit, It doesn't apply much to "Normal" mode, but when the difficulty spikes, It gets barbaric. The only problem I would say I had with the Uncharted games is that they're incredibly linear, but it fits appropriately with the platforming elements. There are a ton of more difficult cover-shooters than Uncharted, but the story, motion-capture and physical struggles that your character goes through make taking cover from open gunfire the only realistic option in this circumstance.