Basically I was curious what was happening lately, sparked in part by today's GOTD, PhotoToFilm. In a nutshell, all the new, innovative stuff seems to be happening in the realms of iOS & Android. That makes sense because most people take pictures nowadays with their cell phones, rather than carrying around a separate camera. It also makes sense because these apps & services use cloud storage, which is where most of those photos wind up. Cell phones don't have gobs of storage, & just trying to find picture files using the equivalent of Windows Explorer is the opposite of fun, so the obvious answer is to have your pics uploaded automatically, often as soon as you take them.
Back at your PC you can manage, edit, download those pics etc., but if for example you want to create a Story using the pictures stored on your Google Drive account, you've got to use the app on your tablet or cell. Windows 10 combined with Onedrive *might* make that sort of thing better, but 10 isn't finished, & Microsoft is still rolling out changes & improvements to Onedrive, along with updating the corresponding mobile apps. Win10's Camera Roll could become the center of that sort of thing on your PC/laptop &/or Windows tablet/cell.
A slideshow based on images stored in the cloud can be a good thing. One, you don't have to actually render your slideshow -- that's done using the service's servers -- so you don't have to worry about what framesize or format to use so that everyone can watch, &/or watch using whatever device or hardware's handy at the time. A significant downside for those folks with real cameras however, is that uploading larger, generally better quality image files can be a big hassle -- most consumer broadband services Very strongly favor downloads, with upload speeds that are significantly reduced.
Another potential gotcha is that moving your collection(s) from one service to another can be a big hassle, e.g. downloading everything & re-uploading to the 2nd account. So if you use something like Shutterfly, where you can order prints, or all sorts of stuff with your pictures printed on it, it's a hassle adding the pictures you took with your cell that are stored with Google. And if you want to just upload your pictures from your cell to Shutterfly, while there is an app, the process doesn't work as well as using Google or Dropbox etc.
Again Microsoft may come to the rescue, but it's IMHO too soon to say... Their efforts with media-related stuff aren't always stellar, e.g. their latest improvements with their re-branded music service app.
Those folks with a Blu-Ray player can most likely put their images on a DVD or Blu-Ray disc, & have the player automatically display them as a slideshow. That works great in the living room at home, &/or when you hand a disc to friends & family that own a Blu-Ray player, but not everyone does -- they haven't come close to the saturation of DVD players in the home.
The next best thing for higher resolution images [including cells with better cameras] is to use a video editor, creating a 1080p or even 4k AVC video file -- of course with 4k you run into a situation where not everyone can watch, though you don't necessarily need a 4k display [downsampled 4k can look Very nice]. You can also do this sort of project in many image editing oriented apps, but most [including Photoshop] are pretty rudimentary when it comes to anything video.
And last you've got the slideshow apps -- nowadays that seems to mean for the most part lower end software that hasn't been updated/upgraded to today's standards. PhotoToFilm for example has potential, in that you can use whatever video codec you've installed in Windows, so you should be able to use something like the x264 VFW codec. Then you get to the drop-down box to set the frame size & see 2 choices, PAL & NTSC DVD frame sizes. Unless you're using an old TV, Why bother? It'll only look good on a lower screen rez small tablet or cell, where you're better off using cloud services anyway.
For choice of video codecs or formats, HD mpg2 VBR can work well, & encodes a lot faster than the better alternative, AVC. AVC VBR is better because more hardware can play it as-is [without adding a player], & for the same quality, files will be smaller. Of course newer formats [e.g. x265] can be used too, as long as you remember more people will not be able to watch. Target bit rate [level of compression] depends on what kind of transitions/FX you add, & if you include any pans &/or zooms -- run short tests & see how low you can go before you start seeing artifacts. That said, a good upper limit would be somewhere around 10 if you want network streaming &/or compatibility with media players &/or streaming devices -- Blu-Ray [& Blu-Ray players] can go up to around 40.