Surprisingly good.
I wasn't expecting much going into this, but it actually turned out to be really entertaining. Tom Cruise was good in it, not playing a typical bad-ass, but a cowardly kind of guy who progresses and develops throughout the film. Emily Blunt was absolutely excellent too.
Similarly to another film I watched recently (Premature), the film utilises the Groundhog Day principle, whereby every time Cruise dies, his day is reset. I'm not spoiling it that much given the tagline for the film is "Live Die Repeat".
But what made this film good was the way it used that familiar device. It never felt boring or belaboured. In fact, it explored so many eventualities and possibilities it made the film feel really fun and fresh. I read afterwards it was based on a Japanese Sci-Fi novel/manga called All You Need Is Kill by Sakurazaka Hiroshi, which explains a lot. There were a few minor plot holes and issued glossed over here and there, but nothing that prevented enjoyment.
I would definitely recommend this. 8/10