A mixed blend of old school WW2, Squad, and Day of Infamy.
With an avid interest in WW2 shooters - Hell Let Loose is a great game with an active development team, working hard to consistently improve their product. It is compared a lot with Post Scriptum (the WW2 game, from the developers of Squad), but to me Hell Let Loose takes the cake.
The gunplay feels inspired by Red Orchestra, which I rate as the best WW2 team-based FPS to date, and the multi-crew tank and fixed-weapon combat is very fulfilling: even when playing as the loader for a heavy artillery piece back at your home base. It feels as if you are contributing to an overall team effort.
As of writing this review, I would highly recommend anyone wishing to get started in more milsim style shooters, especially those disappointed with the release of BFV last year.
TL:DR - A solid FPS with a nice enough community, and historical authenticity.