I have no feedback yet on balance or mechanics because I'm still new and bad.
I would like to see a few improvements to the interface.
First, it's very sluggish in the late game. I'm only playing against three AI's on a medium map, and when we get to level 4 or 5, the response starts to feel laggy. Popups are slow, and commands aren't registered immediately. For example, if I want to sell eighty units of something, I click the sell button rapidly eight times, but only fifty or sixty units are sold. Sometimes when shift- or ctrl-selling, the modifier key isn't detected. This kind of thing is annoying but tolerable in a turn-based game, but a fast-paced game like this needs to be responsive.
Second, my left hand doesn't have enough to do. At the very least, hotkeys should be added for any actions where you would want to have your mouse ready somewhere other than the button, such as targeted black market actions, bulldozing, or opening the rocket menu. I would even like to see hotkeys for each commodity for buying and selling quickly while your mouse is doing other things.
Finally, I think too much information is behind mouse-over popups, which slow the player down. Maybe this is the intention for things like the in/out breakdown of net resource income, which a good player ought to know by keeping track of what he's built, but it is hard to justify for things like opponents' financials. I understand if you want to keep the main screen uncluttered by a lot of these details, or to make the player seek them out as part of playing the game, but I think a set of hotkey-accessible information windows would be a better solution. Or at least switch from mouse-over-and-wait popups to click-for-details popups.
I love the overall design of the game. I've been looking for another Starcraft: a fast-paced, competitive, short-match strategy game that you can play for years and keep improving. OTC has the potential to be it.