I agree that Dragon Age destroyed Drakensang, Alrik, but the reason wasn't 'dark and gritty' - the reason was a combination of compelling characterisation & better class balancing.
If you compare Dragon Age with Drakensang - and I finished (and enjoyed) both games, so I can do that! - the thing that most stands out as the difference is the huge amount of interaction with the characters in your party that is possible in DA, but not in Drakensang. Each character in DA has their own personality, their own personal background quest and their own reasons for being there. All of them can think more or less of you depending on what you do and any of them might leave the group if you do too many things they don't like.
Characterisation for the group in Drakensang was not bad, but it wasn't great either. DA has the best characterisation of any computer game since PS:T.
Class balancing in Drakensang was also very poor, with there being little point in playing either a mage or archer as such characters tended to be overwhelmed in an eyeblink. I liked the combat AI for the enemy, don't get me wrong - they did what I would do and took out the most dangerous people first - but magic was never fast enough or powerful enough to make up for the fact that your mage was going down fast in every fight. Healing spells were a several minute affair in combat and after combat you never needed them, so they were pointless, too. Archers would be lucky to get off a couple of shots before they took a dirt nap, too.
The Witcher should have been a huge warning to makers of RPGs that character depth and moral choice were about to become hugely important, so the writing was on the wall well ahead of Dragon Age. I don't even recall getting to MAKE any choices in Drakensang - none that counted for anything, at least.
Witcher rose from out of nowhere not because it was 'dark and gritty' - that's just a style decision - but because it offered real choice to the player - and real consequences. Dragon Age simply built on that.
Drakensang was a solid enough game, don't get me wrong. As I said, I enjoyed it. I intend to get 2 if it's ever released in an English language version. But it was made with the idea that nothing had changed from 5-6 years ago when CRPGs were pretty much in the doldrums and PS:T was a distant memory. But The Witcher changed everything and Radon's failure to realise that was what ultimately cost Drakensang.
It's not about 'grim & gritty' - High Fantasy would work just as well as Dark Fantasy. It's about player choice, depth of characterisation and (For those whose main emphasis is combat) an engaging and well balanced combat system that involves more than frantically hitting buttons.
Rather than blaming Drakensang's lack of popularity on 'grim & gritty', might I suggest looking at the numerous ways the game could have been improved? It's not always about light vrs dark worlds, you know
As for music, if you want happy/cheerful artists, I can recommend a ton, but you might start with the ever-happy Alex Roots
, the very Summery Eliza Doolittle
and the current number one musical star on planet Earth, the utterly wholesome Taylor Swift
I'd list more, but this post is going long enough already