I myself stopped watching after Slice of Life, though I did make a brief return for Crusaders of the Lost Mark (which I was not a big fan of, especially when it came to Diamond Tiara's rushed redemption). The two-parters tend to take themselves a bit more seriously than the usual slice-of-life fare, so with any luck, the finale will stay focused on delivering a solid core narrative. My expectations are not especially high at this point, but the trailer has me sufficiently excited that I plan to watch the episode.
Given the show's track record at this point, I imagine so (though hopefully it will be toned down, so as not to clash with the more serious tone).
I don't blame you, as the show has definitely struggled with rushed villain redemptions in the past (Discord and Diamond Tiara being prominent examples). The completed S5 cast poster shows Starlight Glimmer standing next to Twilight Sparkle, with a friendly smile upon her face, so I have a feeling that a redemption is probably on its way. With any luck, the execution will be more successful than in past episodes.
I love the idea of a cliffhanger ending (and completing the story in the S6 premiere), but given the show's track record, I find it unlikely. With that said, you could very well be right (after all, the Equestria Girls film was released mid-season, so there is no need to resolve the conflict at the end of S5).
I cannot say that I disagree with your predictions (as this seems to be a trend with the recent seasons). However, I like to go into episodes expecting the best (so as not to colour the experience), so I will put those reservations aside until after I have seen the finale.