Ah, mostly they changed her (GLaDOS)'s character around in Portal 2 to make her more sympathetic, which annoyed me but it was an ok story in itself I guess. I liked her as a villain and as a snarky AI, in general I preferred the first game's aesthetic but don't get me wrong, the sequel was definitely really well done and a dream come true in many ways. The first game was just... perfect imo, so it's hard to compete with that. But I know I'm biased about it lol. Portal 1 was also a lot simpler in a way (and much shorter; it was initially shovelware before it got its, at the time, niche following), yet still amazing, so it's hard to match that level with a sequel when you have to come up with more detail for it, potentially adding stuff that changes the tone etc. I still highly recommend the original tho!!

Also TWEWY does have an amazing OST, and the character designs are awesome, but its story is really what got me hooked- there's some really good writing. I also have Opinions about the anime version where they dropped a lot of detail, but I know that tends to be a thing for adaptations.