Oof, a lot to unpack here, but I’ll try to address a few points without being too long-winded.
The term “weaboo” (weeb for short) is technically a derogatory term for people who are obsessed with Japanese culture, but is often used to insult people who like anime. I’m sure you’ve heard “stupid weeb game” on this forum when people disparage others who like Final Fantasy.
Frieren is animated by Madhouse (my favorite animation studio) and Attack on Titan is animated by Wit Studio and MAPPA. Different studios all have different artists working for them, which gives various shows their charm.
A lot (most?) of anime is based on manga (basically Japanese comic series). Manga authors are both the creators and artists of their manga. When a manga gets adapted into an anime, an animation studio such as the ones listed above handles the production. Different studios all have different artists and animators, so yes their styles will vary greatly.
These are just acronyms. ONA is Original Net Animation, OVA is Original Video Animation. OVAs are often one-offs or spin-offs, and typically have a bit higher production values than series with a lot of episodes. They are typically longer than a standard tv episode as well, and are a form of direct-to-video media.
Isekai means “other/different world” in Japanese. It’s a genre of manga/anime where a normal everyday schmoe gets whisked away to a different world, often a fantasy setting, to interact with that world, oftentimes becoming some kind of hero. Isekai as a genre has become extremely over-saturated in recent years, so a lot of modern anime will be isekai.
No, that’s the actual title of the series - “That Time I Got Reincarnated as a Slime.” Anime and especially the isekai genre has adopted a lot of comically long titles in recent years. Another example of a ridiculous title is “Bofuri: I Don’t Want To Get Hurt So I’ll Max Out My Defense.”
This is based on the 90s manga series Gunnm, known as Battle Angel Alita in the US. There was also a 2-part anime OVA in the 90s simply titled “Battle Angel.” The live-action movie covers the events of the first 3-ish volumes of the manga (there are 5 volumes plus some spinoffs). It’s one of my favs. I’m usually referring to the OVA or the manga when I mention this series, but the live-action film was quite good as far as adaptations go.
The live-action Ghost In The Shell movie with Scarlett Johansson is again based on a manga series from the 90s. There was also an anime tv series called GitS: Stand Alone Complex, and a newer reboot called GitS: Arise, but typically when people mention Ghost In The Shell (me included) they are referring to the 1995 anime feature film, which is a masterpiece. Highly recommend.
Perfect Blue is an anime film (if you are referring to the live-action film Perfect Blue: Yume Nara Sumete, that’s a completely different unrelated movie). Again, one of my favorites. Paprika is from the same director (Satoshi Kon). Both films are animated by Madhouse.
You can refer to my earlier post (#176ish) in this thread about Neon Genesis Evangelion. This is also a classic/masterpiece of anime and has a huge fandom. You can watch the original series and then its two followup films, or you can watch the 4-part reboot film series. All are excellent and ideally you’d want to watch everything at some point if you like it.
As I stated way up in the thread (post #27ish), anime is categorized by not only its genre (fantasy, sci-fi, romance, etc) but also its demographic that it’s marketed towards - shoujo (girl’s), shounen (boy’s), josei (women’s) and seinen (men’s). There can be a lot of overlap, but these are just generalities that can help you pick stuff out and mostly apply to manga and anime shows rather than movies. Perfect Blue for example, I would describe as a seinen/josei psychological horror thriller. Lol.
Hope this helps somewhat, and glad you’re enjoying the world of anime so far!
One of us! One of us!