I like open endings, and even prefer them in many cases. I equate them with ambiguous/somber endings. Perhaps I'm used to them because I used to watch a lot of TV anime, in which the more epic storylines often had less than tidy resolutions to their plots. And that seems to be the direction of primetime drama TV in general since the DVD age, if not before.
Thing is, you have to do it right. You can't usually get away with the open ending more than once. If you continue past that ending, the audience will expect a more literal/final ending next time.
TWOK is a perfect open ending for ST. I've always wanted to see an alternative continuation from that movie, with Saavik becoming a member of the crew in place of Spock... something Meyer might have even been willing to stick around and direct. But I don't think it was ever in the cards. Any possibility of making another movie quickly morphed into "oh sh**, how would we do it without Spock?", and I doubt any other ideas were ever considered. Still there's no reason ST couldn't have ended for good with TWOK. I don't think the classic characters ever evolved further thematically than they already had in that movie.
TSFS is a good exception to the rule of not using the open/ambiguous ending more than once. In this case you're breaking the basic rules of drama by resurrecting a character (I can't blame Meyer for opting out); no one would forgive you if after that you could still have everything perfectly reset. It's a more controversial ending to the series, and I don't think Bennet/Nimoy were ever in danger of not getting another film, but it's not like you 'need' to know the crew returned to Starfleet after recovering Spock. They made their choice to sacrifice their careers for each other; what if that was that?
TVH is your fairly conventional 'reset' ending, already used for TMP, and perfect for closing out the First Generation of ST in all of its self-contained episodic glory. I suspect the general public probably still feels it should have ended here for Shatner and company, and unfortunately I can 'kinda' see that. I also find it a little too convenient that Uhura, Scotty, Checkov and Sulu are willing to sabotage their careers just to return with Kirk to the Enterprise. But it's the right tone thematically, which is why I think it works best as an ending rather than as the start of a continuation. But too late for that.
TUC is very much a product of ST's Second Generation, when every new ST series suddenly needed to have its own 'definite' beginning and end. However it feels contrived in the same way that TVH does, being that Kirk's entire crew -or at least the core 'family', minus Sulu- apparently choose to put aside their careers again just to file their retirement for roughly the same date. Did Checkov really sabotage any chance of ever again serving as somebody's XO? I suppose he did. Who knows. As with Kirk's promotion in the new movie, you kind of just accept it for what it's doing thematically. But in real life ships get decommissioned, people get promoted or transferred, or they retire... it all happens so gradually that you don't even notice it until you're the person who's been here the longest. Which has happened to me a number of times (you can call me Ensign Picard, resident of the 'Tapestry' parallel universe).
Nemesis works fine for me as an ending just as TWOK does... or it would if it didn't feel so clunky, tired and derivative. But I think maybe I'm just not reading it the same way as most people. It couldn't be more clear to me that B4 is not Data, and I have serious difficulty imagining they could've continued painting Brent Spiner's face for another movie anyway. I could be giving Berman and the studio more credit than they deserve, but this time there is no evidence otherwise. I don't recall Nem ever not being the final film and any point in its not-so-eagerly-anticipated development.