It's too bad that you didn't speak up much earlier in the school year -- or probably you did so, but perhaps in smaller ways rather than approaching the teacher for an overall conversation about the big picture, where the teaching seems to be the minimum.
On field trips: Start with a positive. "I just wanted to say that it was a good experience for Johnny to be a peer leader this year (IF that is true), but overall I was disappointed that this class didn't get to go on field trips like the other classes did; why was that the case?" (It isn't clear to me if the other classes you mention "in the same program" are also these integrated classes; if they are not, and are all "typical" kids but don't have special needs kids, is it possible that there was a decision made not to do field trips with the integrated class for reasons of safety or other reasons? I'm not defending that, just saying it's something that could be possible if this is the only integrated classroom. But you should let the preschool know that in future, parents of ALL kids in integrated classes should be told at the start of the year that there will be no field trips!)
On the late opening/early release: I would discuss that at the very next pickup if you have some weeks of preschool left. "Mrs. X, I and other parents have noticed that sometimes the kids have to wait past 9:00 to get iinto the room, and they are going out the door before 12, when parents aren't even in the hallway yet. Could you please be sure to hold the kids until parents are present? It's a safety concern for me" (or whatever applies to the pickup routine, I'm just giving an example).
On the teaching: I would address that with the director. But be careful: As another poster noted, there may be things going on with this teacher of which you are unaware. My daughter's first preschool teacher was kind of blah -- not very engaged. I found out that one of her parents was dying and was ill all through that school year. That knowledge made the parents step back and leave it alone; the kids did fine, she just was not very creative or warm. The kids did not know the difference and thought the year was fun. You could address it with the director along these lines: "I wanted to give you some feedback I'd like you to have about Johnny's year. I have wondered if maybe Mrs. X has some issues outside school because she has seemed rather distant and I find the things the kids are doing seem to be less creative than in other classes here. I hope everything's OK with her but wanted to let you know that we were very disappointed with the curriculum this year (and then add about the field trips)." Any good director will then ask you for details.
It's possible she is so worn out from meeting needs of both typical and special needs kids that she is doing the simplest things she can manage. This kind of mixed class may need someone with more experience than she has. Or she may lack formal training in working with a class like this one. If that is the case, I would urge the school strongly to get her some training, or find a teacher for this class who has training.
And in the end it is one year of preschool. If he feels he had fun, got along well with other kids and learned social skills, and he was in a generally attentive environment, he did OK, even if the time was not as creative as it could have been.