Anyone think up concepts you REALLY wanted to play, but unfortunately don't exist?
Spore.
Just to day, I thought of a game like this:
In most games, when you fail a mission, you get a "GAME OVER" screen and must start again. However, in a game like this, if you lost the plot would adapt accordingly. For example, this mission would be "The attack was successful but they're launching a counterattack, survive until reinforcements arrive and keep at least five troops alive". If you failed to defend the troops, the base would be destroyed and you'd have to flee and assemble a makeshift squad and base as a last resort.
There's only so far you can take that kind of scenario. At some point you will have to hit a "game over" screen and at some point people will decide that they'd rather go back to their last save, before they started fucking up.
In that vein, however, I'd like to see someone make a game based off the Temeraire universe (Naomi Novik's stuff). It'd be somewhere between top-down tactical commander and (I hesitate here, but it's the only technically correct term) a first person shooter.
That is, you strategize before the combat begins, essentially designing your own mission (what part are you playing?) and formulating allied AI response triggers (e.g. this group is going that way, this group is going that way, diversion here, this group serves as backup). And then you fly into combat as a single* unit yourself. It'd be advantageous to retreat if you take heavy damage, in order to avoid losing the scenario, as you're put back in the "command chair" and oversee the AI units in a more RTS fashion ("you might be out, but the battle's not over").
*Single being questionable here. If you're unit is "a tank" you're still effectively playing as three or more people: spotter, driver, gunner, etc. Within the Temeraire universe you'd be the captain of a dragon, but mechanically speaking you'd be controlling the dragon as well as giving orders to the crew (anywhere from 0 to 30 beyond the captain, armed with various things from knives to muskets to iron bombs).