MakeMKV is becoming better and better, but IMO there are still some points that could easily be improved. Especially, finding a specific title is sometimes a nightmare, without a preview. (Finding the longest title is easy, but it's not always what we want to rip.)
1. The information given in the left pane could be more useful if the duration of the title is printed (along with the number of chapters, already present). The file size and number of chapters are good indications to find the main movie, but they are not useful when searching for a specific bonus or episode. The duration gives a much better information. For the same reason, I suggest to print the real title number (as displayed by most DVD/BD players) instead of the internal zero-based title index. (I know that this information is available in the right pane, but it is necessary to select all titles in turn to see it. When there are many titles, it's not easy, and there is no global view.)
2. The default file name has underscores replacing all spaces. Why? All operating systems can handle the spaces, so I see no reason to replace them. Only characters not allowed in file names should be replaced.
3. Also, the name of the DVD or title (retrieved automatically from the DVD-TEXT table) is wrong when there are foreign (accented) characters. The accented characters are removed (and not replaced with underscores). They should be preserved. It seems also that there is a bug. Sometimes, the name is followed by garbage. The strings in the DVD-TEXT table are terminated either by a null byte, or, when there are foreign characters, by a TAB character. Maybe the latter case is not processed correctly.
4. The names of the audio and subpic tracks should be more complete. Currently, only the language is present. In DVDs (I'm not sure for BDs), it is possible to retrieve also the type of the stream from the IFOs: director comments, alt director comments, forced subtitle track, normal captions, etc...
5. Currently, with the new way to specify the streams to keep, it is possible to select them by language and type. But there are some cases where that method doesn't work well. For example, I have selected the French audio and subpics. If I rip a DVD that has no French audio, the french subpic is correctly selected, but no audio stream at all! IMO, when there is only one audio stream, it should be always selected, regardless of the user settings. Similarly, when there are several audio streams but none match the preferred language of the user, the first audio stream should be selected. Who want to watch a movie without audio?
6. The pre-processing of the DVD or BD is sometimes damn slow, especially when there is a lot of small titles, or "complex multiplex". I understand that that slow processing is needed to be able to rip the title successfully, but IMO it is not needed to select the title to rip. Everything needed to show the content of the DVD is in the IFOs. So, I suggest to present immediately the content of the DVD to the user, and to do the slow processing only for the titles he wants to rip. It is useless to scan the titles that the user doesn't want. (It might be more difficult to process DVDs protected with ARccOS or RipGuard, and when it's the case, it may be necessary to scan the DVD immediately, to discover where the real title is, but it is easy to detect that kind of protection by analysing the IFOs only, and when there are not protected, it should be possible to skip the long processing of useless titles.)
If, for any reason, it is not possible to do it, I suggest to change the behaviour of the abort button. I'm not sure what it does currently, but it doesn't completely abort the pre-processing. It will be more useful if the user can abort the pre-processing when the main movie has been discovered (and scanned if necessary). If the user doesn't want to rip also the bonus, it should be enough to scan the main movie. (Another solution would be to add a button to scan the DVD only for the longest title, and ignore the additional VTSses.)
7. Last suggestion: could you add a simple command line, to specify the path of the DVD/BD player or the path of a folder containing the DVD or BD files, and when the path is present in the command line, do the pre-processing immediately, without having to click the big button?
Of course, I second also some suggestions made elsewhere, such as including a preview.
If you wish, I can perhaps help you, especially if yo need some help on the DVD IFOs. I'm the author of PgcEdit, and the IFOs have no secrets for me. (I'm not at all a specialist of the DBs or VOBs and muxing stuff.)