I award you 12 out of 5 stars for authenticity! great, great stuff! it's hard, though. I made it past the second crashed pelican and into the big pink building after three or so tries, but got stuck there (making me miss HALO's checkpoint autosaves but those wouldn't be very Genesis then would they!)
the name is great, because of the double entendre, it's for the Sega Genesis obviously but HALO: Genesis sounds like it could very well be the real name that 343/Bungie would use for a HALO spinoff or prequel!
it's an incredibly minor quibble but I feel like grunts are super tanky bullet sponges when you can't aim for the head. your experiment is a great success. I love that it has sensibly mapped manual reloading, something modern AAA shooters are STILL fucking up to this day. shooting feels awesome, very halo-ey!
a little bit more of a fault is that I wish there were health pickups, it doesn't seem like medkits would have been a difficult thing to add as powerups/pickups to restore some of your health bars
I bet I'll enjoy it even more when I come back later to play it with a game pad, keyboard was a little awkward.