As a healer, I do wish fights were less scripted that way I can heal more reactively, but I don't have a problem with scripted mechanics as a healer thanks to content like Alliance Raids and Bozja. Even though the mechanics are scripted, those who will dodge and will not dodge are not. High end duties as a healer is a different story since nearly all the of the healing requirements are also scripted. For relevant content when the DPS checks are tighter, there isn't a lot of margin for error.

As a DPS, I favor scripted mechanics because it allows me to actually get better at that particular fight. I may notice things like holding off on slapping a vuln+ on the boss because a mechanic that tends to make DPS lose throttle might line up perfectly with it. There is also what I like to call 'a flashy factor' wherein not only do you learn the fight, but you also add some pizazz to it to make yourself look like a seasoned pro.

In any case, I do enjoy when bosses mix things up a bit, and some fights do have a bit of randomness to it that might divert my attention away from my rotation enough to screw it up. Making fights more random would be a change to encounter design. While I don't oppose this, I just know it would be a ton of work for the devs, and there would be a lot of trial and error, hot fixes, and all that.