Disclaimer- This post is about the gameplay of blitz and does not discuss balance, I will discuss balance in a post in the leader feedback section.
I waited until towards the end of the beta to provide my feedback because I wanted to give it some time to see how things developed. The main issues I see are controls/responsiveness, path finding, targeting (especially through the fog of war). In general the team colors are too similar and it can be difficult to distinguish your units from your teammates. A key aspect of halo wars that is missing from this game is team colored cursors on the mini map. Being able to see where your teammates were looking was an important part of the first game and should be included here.
The controls for halo wars 2 should mirror the controls of halo wars 1, and this isn't a matter of trying to live in the past. This means that left trigger should be increased camera speed, left button should be all units, right button should be local units and right trigger should be to tab between unit types. You should be able to set a global rally point by double tapping the left stick. Holding X should set a waypoint. For the purposes of blitz, card selection should be a combination of left trigger and the d-pad, then using either A to play the card or X to cycle. I do like the idea of the control groups, but they need to be implemented without causing delays for the right trigger. In the main game the functionality could be moved to the left trigger instead of the right trigger, but I'm not sure of a best method as it pertains to blitz. Pressing the right stick was always a useless button, perhaps that could pose a solution?
When using the right trigger to cycle between units it was slow and not useful due to the amount of time it took to cycle. This was an important tool in the first game for controlling armies quickly and needs to be fixed. Also after you tab to the end of your units with right trigger it should tab back to the first unit and not to "all units." If someone wanted to select all units, they would just push the all units button.
There are times when units will walk through one another to get through a choke which is nice, but this is not a consistent behavior. When issuing commands to a particular unit in a squad they tend to push the other units in the squad way off course or are prevented from getting to their target location by the other squad units, which becomes an issue when trying to split units effectively.
The locust although a really strong unit in the beta could only walk in one direction. This is fine as a form of check to its strength, but in order for it to turn around it would need to walk in a small semicircular path before it could walk away. When you combine this with some of the tighter chokes on the map it caused the locust to walk great, often comical, distances around obstacles and oftentimes into enemy territory in an attempt to turn around. I don't mind it taking time to turn around but it should probably be able to do it on its own axis instead so it doesn't try to walk around boulders the long way. It's ok for the map to have small chokes, but units need to be able to negotiate them in a reasonable manner.
As a general rule, units should auto target what they are best at killing. It seemed like units prioritized attacking infantry over all else, which doesn't make much sense depending on the scenario. Units should only be able to auto target and attack enemy units that they can see. I'm most specifically talking about the locust in this case. The locust would auto target units through the fog of war with no regard for high ground. The locust wouldn't be as strong if it could only shoot units that it had sight of.