I've played a few rounds so far and it has been...good, but not great. I agree with sentiments that the map is a little on the large side, and not being able to select spawn location makes getting from place to place slow unless you use a vehicle REQ.
Speaking of REQs, I was really excited to be able to use them in a PvE environment, but I think that this mode is too dependant on them. From what I've seen, the vehicle ones are definitely more valuable, while the weapon REQs don't seem to help as much as they should. I don't like how REQ's are needed to win the game over strategic team play or weapon combo selection. The winning strategy seems to be just spamming as many scorpions or wraiths as you can in the final round. If you don't have access to these tools then you will lose.
On the flip side, there is a lot of potential for this game type, and I'm still excited to see what will be done to refine it post-beta.
Here are some things I'd like to see in the final version.
-Limited lives per person to reward strategic play and discourage recklessness.
-Introducing the revive mechanic from campaign would be a cool compliment to the limited lives factor.
-A mixture of smaller maps, where there are no vehicles present, to focus more on gunplay and weapon REQ's, and larger maps that also include more enemy vehicles of the ground and air variety.
-Give a team one or two retries per match.
-Design some friendly AI REQ's that we can call in, like Marines, ODSTs and Spartans, and allow us to use the order mechanic from campaign to direct them around.
-Introduce some more objective types for the player, such as delivering a bomb and arming it or something like that.
-Introduce more boss types, which would add some variety to the final round.
-Introduce some variants, such as unlimited time matches like classic firefight, or firefight games that scale the team size, to as small as four and as large as 12.
-You could introduce a competitive element where Spartans are grouped into Fireteams of four, and they are competing for the highest score against the other Spartan Fireteam(s).
-There could also be a no-REQ variant where Spartans would have to focus on strategic play without resorting to tanking with powerful REQs.
That's all I can think of for now. I'm hoping to see this mode become great, as I having been looking forward to seeing it happen since before Halo 5 launched.