As others have indicated, you don't want to say:
Oh I was almost to forget to mention...
(For one thing, the was is inappropriate there.) Instead, you'd want to use one of these:
Oh, I almost forgot to mention...
Oh, I forgot to mention...
It's interesting how the word almost is optional in this context.
Let's say I meant to tell you that you got some mail. As you're walking out the door, I say:
Wait! I almost forgot to mention: You got a package today.
I almost forgot to mention it – but then I remembered in the nick of time!
Alternatively, I can say:
Wait! I forgot to mention: You got a package today.
This means: I had forgot to mention it (until just now). But now I'll mention it.
At least in AmE, I hear and use both of these. People don't seem to get hung up on whether the almost should be included because, with or without it, the sentence can sound correct.
To keep your tenses consistent, use had for the first case, as it implies that "not seeing a movie like this' is in the past.
For the second case, the first sentence refers to the movie when you watched it, not the movie in general. (Otherwise you would have used "That is a great movie"). Therefore since we are referring to the movie in one of its instances (when you watched it), the second sentence should begin with was. After that, have seems like the logical choice since this phrase I had ever seen is technically describing the movie, and is attributed to the word before it, hence not having its own tense.
However, this is dialogue, and the rules are loosened, particularly because people don't perform this type of analysis before speaking, therefore you are a bit more flexible in this situation.
I know I got a bit technical there; if you need clarification I'd be happy to help.
Best Answer
The text in question 1 is correct: seen occurred before that day, so present perfect simple had seen is the right tense.
The text in question 2 needs a small change: the same change should be made to the original sentence.
When you use the expression ever since, you are talking about something that has been happening for a while, and is still happening. You therefore need to use the present perfect contiunuous have been wondering rather than past continuous was wondering which we normally use about things that have finished.
Note, though, that we use was wondering as a backshift when asking a polite question, for example: