Z

The Good
After I had played Z, all other RTS games looked lackluster. This is not because of fancy graphics, but because of the incredible gameplay. No other RTS keeps you on your heels like Z does:

There is no cozy buildup phase. - You are in the thick of it from t=0 onwards.

There is no room for errors. - You have to enter a map with a battle plan, or you will be crushed.

There are few units on the battlefield. - You need to take good care of yours, as high casualties cannot easily be compensated.

Besides the gameplay, there is the tongue in cheek atmosphere of the game, which kept me hooked, even after a lost a map for the nth time.

The Bad
Z is challenging. There is no one size for all strategy, which works on every map. This means that you will likely get your bottom handed to you far more often than you are used to from other games.

The Bottom Line
Z is as close to pure adrenaline, as you can get in a RTS.