There really isn't much of a tech tree in the game. Players can typically research nearly every upgrade for weapons, soldiers and bases in the span of one match (against the computer, specifically), so I never got the impression that I needed to decide where I should focus my time. Units only have between one and five upgrades -- that may sound like a lot, but research completes rather quickly, and eventually you'll be left with nothing to spend resources on.
It's the kind of suspension of disbelief that you'll snicker at.
The mechanics in the context of the story work, and I enjoy how resources are collected, but the process does make you scratch your head at times. The best example is upgrading your mother ship, the Spirit of Fire. Since most resources come from the mother ship, upgrading it means the Spirit of Fire has to first send resources to the planet surface where they are then collected and spent on upgrading the ship. It's the kind of suspension of disbelief that you'll snicker at.
In the end, I had a lot of fun with Halo Wars. Sure, I have gripes, but it's a simple experience that may appeal to non-RTS fans, and even to hardcore RTS players who keep in mind that the game isn't trying to be a PC title.