First off, I want to say how much I am enjoying the game. After playing through all of the tutorials (and finally beating the scientific HQ tutorial) I have some thoughts on the gameplay and some ideas to balance a few things out.
1) Buyouts seem to be overpowered. I understand this is how you win the game (although I hope it becomes just one of many 'victory types' in the future) but it seems like one person runs away with the game and there is not much that can be done to stop it. One solution I have though of would be for a buyout to happen over the course of say, 5 minutes, where a player can put up an investment of the full buyout amount, and every 30 seconds they gain control of 10% of the total shares. This would allow the player being bought out to increase their share price by buying other stocks, paying down debt, etc, and would prevent an 'instant buyout' (it would be more along the lines of a Vanderbilt style hostile takeover, I don't really want to sell the stocks in my own company, why should they be able to instantly buy all of them?) This would result in the buying player not being able to take full control of the company if the stock prices rise, or the player is able to buy back the stock in time.
2) Debt seems uncontrolled. Other than taking a ding to my stock prices, why would I not win every auction and let my debt soar? One possible option is to add an additional number under the debt which shows it as a percentage of your total worth, and if your debt exceeds your worth you lose. (perhaps leaving buildings to be purchased by other players, ala liquidation sale style? or they go up for auction to pay back your investors?) Another mechanic of debt is in regards to stocks, as a player can carry a quarter of a million in debt and sell resources to buy shares in another company. Perhaps before being able to purchase shares a player should be required to get their debt under control? If you are spending 300k to buy me out, you should first have to resolve (some?) of your own debt.
3) In line with the stocks, players can buy out opponents even if those opponents control 90% of their company. Shouldn't a player need majority control over their own company before they can buy out a competitor? perhaps allowing a player to purchase back individual blocks of shares (as is now at double value), and then 'freezing' those shares for 30 seconds to a minute before they can be bought out again?
Another mechanic which could be used to help balance the game is the idea of taxes or upkeep/repair/permit renewal fees, increasing with each HQ level to help even out the endgame.
Again, just some first thoughts on things I think could really help the game, I would love to hear others thoughts on these along with other ideas to help balance and improve the gameplay.