This is a series that has been in a constant state of being "in-development" since 2013, changing hands between countless high profile showrunners and TV networks/streaming services. Once it finally entered production in 2019, it has taken nearly 2-years to get to the screen. And then there's the reported near $100 million budget for just the first season.
To say this show is a highly anticipated curiosity is an understatement. I doubt there's a serious critic working today who wasn't at least curious to know what this show looks like. And so when critics finally did get a look at it, there was an overwhelming sense of:
"Is that it?"
And to be fair, they're not really wrong in being underwhelmed.
Halo is set in the distant future - the year 2552. Humans have spread themselves across the universe and not all is harmonious politically. Some humans on the planet Madrigal have been fighting for independence, but as the show begins they receive a visit from a third-party: the tall, big-ass Alien Covenant. An army of Earth's finest, the super-soldier "Spartans" rock up and defeat the Alien Covenant, emerging from the wreckage and pile of bodies of casualties.
There's just one survivor from the, I guess they're called Madrigallians? Beats me, to be honest. My attention had started drifting by this stage. But during the flight home, the head of the Spartans, Master Chief John 117 (which I think may have been a character in Midnight Cowboy), goes rogue. He realises there is a plot by the government to kill the lone survivor, a plucky teenage girl. So the two are off on the run together.
Immediately, this seems reminiscent of The Mandalorian, with the story of a helmeted soldier looking after a child. One can't help but wonder if the pivot away from that dynamic by the end of the second episode was a last-moment re-write when it became apparent that the show was going to be standing in the shadow of the highly successful Star Wars series.

The biggest problem Halo has isn't that it is underwhelming - that's only really an issue based on your own expectations going in. A show needs to be appreciated for what it is and not what it is anticipated as being. The problem is that the show doesn't feel fresh or innovative in any sense.
The show never quite escapes its video game trappings (the battle suits look clunky and uninviting on screen - they're fine for an interactive shooter, but less so for a TV show) and its efforts to give the world of Halo greater texture with interpersonal tensions and political maneuvering comes off as third-rate Game of Thrones style palace intrigue.
Ultimately, what the show is left at is feeling a bit generic with a visual style and plotting structure that seems in line with the modern Star Trek series like Discovery. In that context, Halo is a perfect fit on Paramount+, complementing its Star Trek series nicely. But what it isn't is a broad enough drama that will interest enough viewers to become a crossover hit.
Some reviews will brand the show as yet another video game adaptation failure. That's actually lazy and isn't entirely fair. But at the same time, this show is far from a success. I know it will have its fans. There just won't be as many of them as one might have hoped considering the pre-release efforts to make the show happen.
Halo debuts March 24 on Paramount+