From what little gameplay I've seen, Haggar looked like a lot of fun. And I'm a bit disappointed that it never came to be.
The boarding of the Hunter looked cool as heck (of course)!
And the customization of your Warthog was a cool feature. I dunno if it was just going to be for the Warthog, but being able to drive a Tundra Mongoose or a Banished Ghost, etc... would've been cool too, even if it was just a cosmetic option.
I take it the ONI REAP-X vehicles were all going to be in this game? Since they've been created, only the Kestrel has been in any Halo titles (Spartan Strike). This would explain why they were created, made canon, and never appeared again. Dang shame too; They're really cool (especially the Walker).
I remember way back when LEGO Halo was talked about, and so many people wanted it to happen, but alas it never came to be. And now the same thing is happening with Mega Bloks Halo. I'd say that there's definitely an interest/demand for this style of game, even to this day.
Of course, there'd definitely be backlash and criticism (as always when it comes to Halo spin-offs). And it wouldn't make the amount of money that a typical Halo title would. So I can understand if one of the reasons it was cancelled was because of this. But it would've marketed Mega Bloks pretty well, and expand Halo's audience, which would probably pay off in the end. I dunno.
But the fact that it was something being thought of is extremely cool, and honestly appreciated that you guys are willing to think of taking risks like that and explore Halo outside of its comfort zone.
One thing that would've been cool as heck is if it worked like the LEGO games where after you completed a level, you could go back and play as other characters (after you've unlocked them, of course). This would open up so many possibilities that any other Halo title has not allowed yet. You could play as a Grunt, Hunter, Flood, Sentinel, Promethean Knight, Sergeant Johnson, Tarturas, etc. Which would just be the coolest freaking thing.
Just the thought of playing as an Elite Honor Guard, running around with an Energy Stave, makes me so happy to just think about.
Basically, the sandbox for this game could've been huge!
I can't say Haggar is a game that I need in my life, to be completely honest. But dangit is it a game that I want in my life.
Oh, and I gotta say, it's pretty cool for you guys to acknowledge this game.