I'm neutral on Pikachu, I don't hate it but I'm not a huge fan of it either. Despite this, I feel it does work as a mascot because it's both cool and cute as well as it being relatively easy to draw because of its simplicity.
I like the entirety of the Pikachu line. I especially love Raichu, but I've always felt it was the most under represented of the line. That being said I was pleasantly surprised to see it get some love when they came out with Alolan Raichu. The only thing that annoys me about Pikachu are the copies of it they make every new generation.
Pikachu as a Pokémon is OK. Not one of my favorite but I don't particularly dislike it either. It's cute and fun, and Pikachu as a character is cool too. I liked the story it got on season one of the anime and how it seems like he uses "Pika Pi" when referring to Ash.
I kind of used to despise Pikachu? But I don't know, these days I'm pretty fine with it. I've started collecting a lot of Pikachu merch, so I guess I like him quite a lot more these days than I used to. I might try using one if I restart any Pokemon games from the previous generations, maybe, it has been quite a long time since I've used a Pikachu in battle...
I think Pikachu is absolutely adorable! I love Pikachu's contribution specifically in the anime, its bond with Ash is heartwarming to see! Also, I don't think there could be a better mascot for the brand. However, I do feel that Pichu and Raichu are somewhat underrepresented in comparison to Pikachu.
Unlike some, I actually am fond of the Pikachu "copies" that are introduced in each region. This is because I don't really see them as rip-offs of Pikachu and I think that the majority of them have interesting design concepts. Pachirisu is my favourite by far, it's just a bundle of cuteness.