So we're almost to episode 50. Here's my thoughts on the current pokemon:
Snowy -- I have no idea where they're going with this thing. It's a baby, but sometimes they evolve or prove to be strong battlers. Alolan Ninetales is very popular, but I get the vibe that it's more of a mascot like Axew or pre-Advanced Generation Togepi. We'll see. At the very least, I hope it gains a new move in the next year.
Steenee -- Very bland. They need to give her something to do. She's like her trainer and feels more like an afterthought than anything.
Turtonator -- Solid enough for the moment. I also am glad to see proof that "big" Pokemon can be out of their balls fairly often and contribute to the humor.
Marowak -- Not done much, but the personality is truly brilliant and I just want to see more. I also find it interesting how it was caught with a full moveset
Popplio -- Surprisingly good development considering Lana doesn't have an active battling goal. The use of the bubbles is creative and I enjoy watching its progress. I see Brionne in its future and hope desperately for Primarina.
Togedemaru -- Cute but not much else.
Charjabug -- Its existence was justified purely by episode 41. I wonder if they'll evolve it when Vikavolt happens in the games.
Lycanroc -- USUM promotion, the Pokemon. They at least let it keep Rockruff's personality, so that's mildly interesting. I imagine it won't be that long before Ash get is exclusive Z-Crystal.
Litten -- As has been mentioned in the thread, it's not had much battle experience. It's had some good character development, but hopefully it gets a good battle in when Ash does his next trial. I see Torracat in its future and potentially Incineroar since they often evolve Ash's pokemon to their bipedal evolution. Though it's probably too early to say.
Rowlet -- I am so mixed on this thing. Battles a lot, but has had the same three moves since capture and is used more cuteness than development. I won't even try to guess what'll happen with it. Its battle style is a nice adaptation of the game Pokedex entries and official artwork and I find it to be the most interesting of Ash's current team since there are a lot of directions they can go with it.
Nebby -- Togepi and Larvitar's reincarnation. At least this one is necessary for the games' plot.
Pikachu -- Has a solid portrayal this gen.
If it counts, Rotomdex -- I'm kind of disappointed that Rotom seems to be unable to understand other pokemon. It makes it feel more like just a regular AI.
Edited to Add: Do we think Gladion is going to be a league rival or just a story rival? Because at the moment, I can't tell if they're going to give Gladion a full team or not. Sure, they could add Crobat, Lucario, and Weavile to his current team but I feel like Gladion and Ash will mainly have 1 vs 1 battles anyway. I get the vibe that next year or so we'll meet another rival (Hau or anime only) who's working toward a full team and has one of the starters while Gladion will be left as Ash's main source of conflict for the Ultra Beast plot.
Also may as well add other recurring Pokemon:
Mareanie -- The 'glomping Pokemon' escalated to outright having a crush on James. Sadly though, besides helping beat Ash once, it hasn't had much substance otherwise. Like it's trainer, it needs more individual focus.
Mimikyu -- A unique addition, since it's a sinister Pokemon that uses Team Rocket more than obeys them and is a powerful little sadist that wants Pikachu's blood. It's begrudged care for Jessie and it's 'wants to be loved' shtick in the games opens up potential development for both of them though. Needs to have a more developed battles with Pikachu too.
Meowth -- Like that he's battling more often (even if it's predictably fruitless most of the time). Recent episodes hint to his reflexes getting better, would LOVE if he actually got a boost for the first time. Otherwise has the same highs and lows as the rest of the TRio, which is a better series for them.
Wobbuffet -- Funny as usual and a bit more expressive. Sad to see him completely inactive though, especially after the badass he was in early XY. Come on Jessie, use Counter at least once this series.
Bewear -- Mysterious Pokemon, will be interested in seeing where they take it's character, until then it's gag is pretty funny and has more longevity than blasting off all the time. I just hope they don't use it to cop out of having any developed TR face-offs all the time.
I also think it's kind of a shame we don't see more of Samson Oak besides his punnery. His Komala and Vulpix seem like they could be enjoyable.