I meant to write this post for a while now, but 6233638 already covered many of my gripes, so instead of hijacking his thread, I'll just add here a few more things, mostly related to video, that I consider it's worth addressing. Please don't get me wrong, I think MC is amazing in most respects, and maybe that's why its few shortcomings feel so sore at times. Feel free to correct me where I'm wrong, and please do excuse my english.
General
1. Find and Replace is a blanket operation; in fact it should allow for skipping certain instances.
2. It would be great if we could mark specific pairs of files to no longer appear together in smartlists (eg dupes etc). There's an excellent way to do this in Calibre, so I guess it's feasible.
3. The wiki needs to be updated and expanded. A noob has no other way to find out what's possible in MC. At some point I spent countless hours manually cleaning up parts of fields, before I incidentally found out in the forum that there were ways to do it automatically.
4. ...And as I wrote elsewhere recently, it would be great if somehow all the tried expressions, views, smartlists etc that people have created over time were collected, sorted and made available for noobs - either in the wiki or preferably in MC itself. E.g. simple append/prepend operations, so common in tags editing, should be readily available from menus and not only through a cryptic syntax in the Tags window.
Importing
5. When importing video files, or while using the "Fill Properties From Filename", it would be helpful if MC could locate existing external subtitles and auto fill a custom field [Subs], possibly based on the naming structure (Dir - Title - Year - SubLang.srt). That should even be easier for subtitle streams embedded in MKVs.
Scraping
This is an area that needs to be the focus of serious effort. Even if legal problems don't permit the use of sources like IMDB, there are still ways to improve it. For example,
6. Scraping TMDB with multiple files selected does not take into account the [Year], so MC just picks up data for the first available title (usually the most recent), which results in the wrong info being stored: Raw Deal (1986) is preferred to Raw Deal (1948). Ideally, Get Movie Info should collect the correct film based on the pair [Title] - [Year] or at least offer us an opportunity to disambiguate (just like it happens when we scrape single files).
7. Similarly, when multiple files are scraped, if a title is not an exact match, it is skipped. I miss an option to pause and reshape the search term. As it is now, we have to manually search for each of the files not exactly matched in the first run.
8. While scraping, there's no way to selectively add info from sites; it's either Get All Fields or None At All. If it's too difficult to include tick boxes to select the fields to keep, you could at least include a "Fill Only Empty Fields" option.
9. (I'm not really sure about this one.) When the wrong info is imported, we can't clean all affected fields in one fell swoop. Esp. List type fields (Actors, Genre, Keywords etc) need manual unticking of all the unwanted info which is tedious. Ideally, the Clean File Properties window should have a "Clean All Field Contents" option, to purge all imported data on selected fields. If that's not possible, at least an option to "Clean all fields except the file related info" (FPS, file size etc).
Theater View
10. Customizing the Info Panel should become even more flexible. I would love it if we could squeeze 2 or more short fields in one line (FPS, Duration etc) and change individual field/letter sizes, so as to minimize the need for scrolling.
11. I would have liked a more flexible Theater View. Among other things I miss is an on-off keyboard shortcut to show captions or not, and a way to show bigger thumbnails (Ctrl+Mouse wheel really changes the letter size and only relatively the thumbs, and this only up to a point).
11b. BTW Am I the only on to consider Ctrl+Mouse wheel counter-intuitive? In image apps, rolling the wheel forward zooms in (magnifies), in MC it's the opposite.
12. I'd love to see more video sites accessed through Theater View - maybe under a menu that would include YouTube, Vimeo, DailyMotion etc, ideally taking advantage of Couch Mode options.
13. BTW, at the end of YouTube files played in my browser I get a thumbnail list of possibly related videos; why is this not available when watching the same video in Theater View You Tube?
14. Just a wild thought: how difficult is it to implement "hot links" in Theater View? Wouldn't it be great to click on an actor in Info panel and jump to a list of his movies, or to click on a keyword to bring up a pane with all related videos?
And a cautionary note
15. When I first cami into MC, using the "Rename, Move & Copy" to restructure my library caused me long hours of work when I found out that all image files in my music folders were not moved along with my music. And although it certainly was my mistake, I think that until moving entire folder contents is available, it would be safer if the users were informed on the fly of the possible consequences.