This is surprisingly good. Definitely not the movie for the ages, but as a comedy-horror flick - top notch. The story is laid out really good, and has actual plot twists, that I did not expect, to be honest. Characters are interesting, even though they are still rather cliched. Great pacing, that does not make you feel bored at any point.
Great casting, younger and older actors do look quite similar to each other, which definitely adds with the immersion: something that is often glossed over. It's not as uncanny as "Dark", of course, but still really good. And they do play their roles well, too.
Interestingly, I am not sure if I saw another media with a similar approach to time travel. The concept of "river" is a familiar one, but the way it's implemented and integrated into the story feels unique. It does not feel like a gimmick, you know. It's not sciency by a longshot, but it does make sense, as well as the ending - the approach they took for it would definitely be useful for anyone else working on something similar.
Definitely recommend, although manage your expectations, since this is closer to a b-movie, even though a very solid one. If you do - you may even see a strong moral message behind the occasional silliness.