I'm personally not a fan of those changes. I understand that rotating viewfinder is more natural (you are shooting from Aya's perspective, after all) and that diagonal shooting in StB could be seen as cheesing, but for the former there is a problem I will mention once I get to atmosphere, while the latter in my opinion is an example of developing specific tactics to the game mechanics, rather than exploiting an oversight. I think so, because it feels like ZUN wanted to keep angling viable via point multiplier in DS, but this is much cruder tool that misses what was good about angling in StB. The countermeasure of two shooting modes is somewhat awkward as well. There are spellcards where portrait mode is almost mandatory to survive, while I've never encountered a spellcard in which horizontal mode was a safer option. But at the same time, apart from those few spellcards designed for portrait mode, it often felt as if I was heavily losing on points when I used portrait instead of horizontal. Once I figured out the spellcard, there was little point to not using horizontal. This issue (portrait being safe but point-starved and horizontal being the opposite) is even more pronounced on Hatate, which has a smaller viewfinder and can't move it as much as Aya after entering photo mode. There should be greater variety in spellcard design to accommodate both modes in my opinion, so that you have an incentive to switch them more often both between different scenes and in the middle of them. But if someones struggles with the difficulty in the later levels portrait mode is surely a blessing.
Speaking of spellcards, DS has more of them, not to mention that you are supposed to complete almost all of them at least twice, once for Aya and once for Hatate. The differences in playstyle are notable. As I mentioned, Hatate has smaller viewfinder and can move it less, which immediately throws you of. Even with how I played aggressively with Aya mostly on horizontal for those sweet, sweet points, just a fraction of a second for a little movement of viewfinder is often enough to keep safe distance if you need it. On Hatate you either get the distance right from the start or you probably should make a defensive photo that clears bullets without catching boss. It also plays into Hatate's strength of getting more charge % on photos and also having higher cap. In StB, successful photo can charge you up to 30%, while unsuccessful can charge up to 60%, depending on how many bullets you catch. In DS, Aya keeps 30% for successful, but gets only up to 55% on unsuccessful. This 5% difference can be quite problematic, I've certainly tried making less defensive photos with Aya in DS due to this. Hatate gets charged up to 75% for unsuccessful photos and up to amazing 60% for successful photos. For spellcards expecting you to keep charging up, like 6-7 or 10-1, it completely trivializes the challenge that Aya faces and is quite big on other spellcards too. Final difference between reporters is that Hatate's crosshair always seeks the boss. ZUN says it is Hatate's advantage, I disagree. For most situations pressing shift to put crosshair on boss moment before the photo is good enough and there are some spellcards where getting boss off-center can be quite helpful. For instance, my clear of EX-9 with Aya exploited moving a bit backwards after almost hugging Sanae before shooting in order to clear more bullets and have an easier time escaping. I still haven't cleared it with Hatate, but I know I won't be able to do similar trick.
The spellcards themselves are fine in both games. There are fun patterns, there are hard patters, there are patterns that are both, there are patterns that will make you question if you aren't pathetic, hopeless and not cut for danmaku games, there are finally some duds that are too easy and uninteresting. DS have few more of the latter, but I think this is simply a result of having more spellcards in general. A great thing about photo games is that once you clear boring scenes, which shouldn't be a problem, you can ignore them and keep having fun with better ones. Both games also include gimmicks in some scenes that aren't straight up parts of patterns. In StB, if a character has a gimmick, it usually is explored in various ways throughout their spellcards. For example Youmu's slow-motion or Sakuya's timestop, gimmicks that if they aren't repeating, then they will at least be rhyming through spellcards of that 2hu. Clearing one scene with any of those allows you to know what to expect in others. DS has many one-of gimmicks that aren't used later on even by the same character, for example Murasa's phasing in 5-8 or Byakuren's talismans turning into swords instead of being cancelled in 12-7. The only exception that I can think of would be Orin having zombie fairies reacting the same way to being photographed in two of her spellcards. It adds surprise, but it detracts somewhat from coherence, when compared to StB.