What has been your overall experience with large introductory science classes as a student

Depends on topic.

If it's humanities, social sciences, or biological sciences, you are wasting your time in large intro classes. Try to write to the professors in higher levels and see if you can't skip the lower levels. The faster you reach high level coursework, the better. You know you've hit high level coursework when your assigned readings are primary literature and your turned-in assignments have primary literature citations. You can make up any missed knowledge on the fly with a simple google search.

If it's chemistry, computer science, or anything quantitative (physics, math, engineering) then you need to sit though the intro course if you aren't totally confident that you know the material, because the next course will be extremely cumulative on the knowledge you gain here.

(I may be biased, since most of my interests have been in biological/social sciences and so I might just have known more about those things starting out).

I tested out of most of the introductory general required classes in undergrad. My undergraduate degree is in engineering. My department's introductory classes generally were broken into multiple sections of about 30 students, so my experience here is perhaps not representative. The 4 large (100+ student) classes I took were in the math and physics departments.

In the physics classes (which were specifically for engineers, not physicists), the actual topics were dumbed down so much that I had to modify my thinking to do well in the class. And I found the classes to be dreadfully boring in general because the more interesting topics that used math were avoided. Anything involving more than the simplest calculus was avoided. If I could think of a way to do something involving differential equations, surely that was not what the professor wanted. I often had difficulty figuring out why certain (unnecessary) assumptions were made, and I came to the conclusion that they were made to make the class more manageable for the least capable students. Often which assumption to use was ambiguous because any number of bad assumptions could be made.

My experience here is that these classes were designed for the lowest common denominator, and with a large sample size your probability of having someone who'll really hold back the class is near 1. Often this worked to the detriment of the most capable students. I speculate this was done because the engineering school wants to produce more engineers. Seems that their main approach to this is to dumb down classes. I'm somewhat convinced this does more harm than good, partly because I think most of the least capable students would struggle no matter what they were given, though I don't have strong justification for these beliefs at the moment.

Another impression I got from the physics classes was that the professors didn't want to teach these classes. They seemed to consider it a chore, like taking out the trash. There was no consistency between semesters or years in who taught these classes. I'd guess the physics department required professors to teach these introductory classes on a rotating basis, i.e. "It's your turn to take out the trash." There was no passion in these classes, which contrasted heavily with the one upper-level physics class I took.

This did not change my desire to become an engineer. I would fill in gaps in my knowledge on my own time. These classes mostly harmed my time efficiency.

One of these classes required me to buy a clicker, but it never was used in the class. One of the courses used some online homework thing that I thought was dreadful, mostly because I had a difficult time thinking in the constrained way they wanted me to, and also because some of the answers in there were wrong! These courses used Blackboard to manage the other course content, but I didn't use any of the advanced features. I recall downloading assignments and checking my grades.

The large math classes (calculus and differential equations) were for all majors (including math majors) and I didn't feel the topics were dumbed down or that the professors didn't want to be there. My impression was that the professors were not concerned that people couldn't keep up. If a student couldn't keep up, that was their problem. I think this might have partially motivated me to take more elective math classes than physics classes during undergrad (2 undergrad + 1 grad math class vs. 1 undergrad physics class), but applied math is more my interest, anyway.

The math classes had their own websites. No advanced things like clickers or Blackboard were used.

I found the textbooks for the physics classes to be poor jumping off points for more advanced topics. Once you understood calculus, there was little reason to read these books. They also were basically worth no money after the class was over. I vaguely recall throwing mine away because they were so worthless. In contrast, I still own and sometimes refer to my calculus and differential equations books.