Good Question !
I will try to answer it..
Firstly the LCD2 is dark sounding, you could say veiled...
The LCD3 isnt, its lively, faster, more fun .. The L2 is fast fun and has good PRAT
The LCD2;s balance was more to bass and mids, the highs restrained..
The LCD3 is better balanced across the range with neither lows,mids,highs talking centre stage ( they have acheived this by making the highs much better while the bass and mids are at least just as good as the LCD2, I personally think quite a bit better IMO..
The soundstage on the LCD2 was quite small, personal... great for some music
The soundstage on the LCD3 is bigger wider, deeper, and instruments are better placed... The L2 has a wide, deep soundstage too..
Muddy ????? not sure about muddy
The sound on the LCD3 is better integrated than the L2, both cans will go loud, the LCD just a tad louder..
The LCD2 could have been accused of being muddled I guess having now spent time with the LCD3....in comparison between the L2 and LCD2 , that darkness could be confused with muddle
If i hadn't heard the 3 ... i would have said it was brilliant....
Both the LCD2 and LCD3 are better phones than the L2.... not £800 and £1800 respectively mind...
The law of diminishing returns !!!