Don't make a drinking game out of the random panty shots in Thigh-Rise Invasion (pun intended). It won't turn out well for your health.
High-Rise Invasion has an interesting premise and a very strong start, filled with mystery and suspense, but as it went on, those aspects decreased and the flaws of the show became more apparent.
This anime is about a group of people who are suddenly thrust into a bizarre world and need to find a way out. This is actually very similar to the live action Japanese TV show that aired on Netflix a little while back called Alice in Borderland. Definitely give that show a watch, as it's very good (it also has an English audio option). The immediate mystery creates a huge draw for the series, and you are instantly put into the character's place trying to figure everything out, just like the characters are.
One of the aforementioned flaws in this anime was the animation. Studio Zero-G isn't a well known giant in the industry. In fact, I haven't seen any other anime from that studio so I can't say how well it matches compared to their previous work, but the animation for High-Rise Invasion, while clean, was a little lazy. Both in and out of action sequences. Nothing looked bad, but it is a shame that this show couldn't be given to a more well known animation studio. There were no flashy moments of sakuga and even regular movements seemed off sometimes. There were also some bad CGI integrations that really seemed out of place. That being said, the character designs were nice at least.
Animation alone doesn't always make or break a show though and while the animation by itself might not have been the shows strong suit, it wasn't the only flaw in the show. The characters themselves weren't that well developed. Some were given backstories that took themselves too seriously considering some of the shows goofiness and other characters backstories were somehow too ridiculous even considering the rest of the show. On that note, the tone of the show was all over the place. The show at times doesn't know if it wanted to be taken seriously or not. One minute a person could be beheaded in a supposed to be sad moment, and the next, there is an "accidental" panty shot.
That brings up the biggest flaw, the fan-service. I don't mind fan-service if there is a point to it in the narrative, but there really wasn't any point to it here. It was just a way to reach a certain viewing audience and sell better to that crowd. Every episode there were multiple panty shots and there were a few nearly nude scenes thrown in though nothing explicit is shown. There is also some Yuri subtext in between the two main leads which leads nowhere but will appeal to a large viewership nonetheless.
The music in the anime did its job. The OP is done by Empire, so those who watch Black Clover might recognize the artist. It took a few listens, but I ended up really liking the OP. The ED is mostly forgettable though. The OST did its job and really hyped up the scenes to be epic when needed. The voice acting (English Dub) was pretty good as well.
While the story starts off really strong, as it goes on, the plot sort of becomes a mess, many things don't make sense, and since it ended off unfinished and needed a second season, lots of questions remain to be answered.
All that being said, this show was a lot of fun. Some of the lines in fact would have fit right in an abridged series. Like "I recognize those panties anywhere" (paraphrasing). High-Rise Invasion is just a funny brainless popcorn flick at times, and a suspenseful thrilling mystery at others. The sum of its parts don't equal out to the whole for this anime. While there are big flaws and not so many strengths, it really is an enjoyable anime. Whether you enjoy it ironically or not is up to others to decide for themselves, but I had a blast watching it. I might even watch it again with my siblings and laugh with them about it.
In the end really, the over-the-top ridiculousness may be what makes or breaks the show for you. Some people might think of parts of the show as too dumb while others might think of it as dumb but fun.
Overall, I am rating High-Rise Invasion an 8. There were too many flaws to score higher than that, but it was also too enjoyable and fun to give a lower score. I haven't watched an anime as enjoyable as this in a while, so I guess that is my recommendation. Watch it and then either praise it or bash it, as long as you have fun doing so then you got something out of it.
P.S. Only calling this anime Thigh-Rise Invasion from this moment on.