I seem to run into "help I have no more shows to review and no time!" around this time every year actually, usually I pull a short or two out fill the space and that's exactly what I did with the Thermae Romae anime last year (it's since been licensed by Discotek although I'm unsure if it's streaming). I enjoyed it more than I expected so when the JICC announced they were having a showing of the live action movie I couldn't resist. It was a comedy to start with and with how over-acted Japanese live action comedies tend to be I couldn't wait to see how it turned out.
As a quick note, I still have no read the manga (licensed by Yen Press) so while I believe that the second part of this movie is original, it wasn't in the anime, I could be wrong. It felt like a new addition however, while the first part of the movie matches up closely with the anime it introduces a reoccurring character in Japan, young Mami who seems to always be around when Lucius pops up and quickly develops a crush on this muscular, mostly-naked, man. The plot also brings in more Roman history than the, admittedly rather short, anime adaptation did by having Lucius become more involved with Emperor Hadrian and eventually the fate of Roman history rests on his baths which certainly feels more like a movie-style plot than a manga-style one.
Regardless, while I felt like Mami was a bit pointless and her overacting was the only bit of acting in the film that annoyed me (everyone else was toned down just a bit, or at least didn't flail around as much during their awkward scenes), I really enjoyed this movie and I think I liked it a tad bit more than the anime. The humor worked really well in the live-action context and my showing laughed a number of times and was practically in stitches in what can only be described as "Lucius has a religious experience concerning a bidet". There were many little funny moments, a running gag involving the background opera-singer that accompanied Lucius transition between worlds, special effects that seemed to consist of taking figures of the actors and flushing them down a toilet to also convey traveling between time periods, and a few truly random, bizarre scenes but not so many that the movie fell apart. The budget wasn't terrible either actually, aforementioned special effects to the contrary, and while there were some scenes which made me think "oh this was the b-roll" the settings looked convincing enough and when a scene needed a strong visual it was right there and on top of it. I was curious if some of the actors were dubbed over however, there were one or two background actors where the lip flaps didn't quite seem to match up and the audio sounded a bit off but this was only in a few scenes so it's not a major concern.
When it's all said and done, you can easily watch this movie regardless of how familiar you already are with the story provided that you are willing to be convinced that a movie about Japanese and Roman baths can be silly. It's very much a B-movie but one that is aware of it's own silliness and just wants the audience to laugh along with it.