I tried Halo 5 for the first time during the free period with the presumption that I'd buy it afterwards, but I was surprised to find that I didn't enjoy it at all. I've never been a Halo purist and I loved Reach and Halo 4, but Halo 5 just felt odd for me. It might have been because I was out of practice for so long, I dunno. Didn't get the chance to try Firefight. I hated the whole REQ packs system, I was disappointed in the direction of the story, and all the armor pieces looked like unrecognizable 3d meshes with no real heart or personality. Hell, even Forge managed to feel more like an editing tool than a sandbox gamemode, which I suppose is good for content creators but as a casual Forge user I felt overwhelmed with the new UI and features (which is really my own fault for not spending more than 20 minutes to absorb it all). I really wanted to like Halo 5, but I just didn't.
I'm glad to hear the game has legs and a lively community, though. Even if I didn't like this iteration I think Halo has room to grow and hopefully whatever the devs cook up next draws me back in.