Try approaching the encounter with different tactics in mind.
Instead of bunching your party together in a narrow defile (I mean, it's a classic ambush scene right from the start, but you can see from the top of the path the options availible to you.) split them up, get ranged up on the paths, remember to use Lae'zels jump ability, or Misty Step, and some of the Illithid powers are useful here too.
I love this fight because it adds height into the equation, and the enemy is a master at the height advantage and more mobile than you so you have to fight smart.
For every part of the game: Explore, experiment (save often!), use tactics, and adapt.