This week I've been playing around with Hazardous Software's strange RTS concept, Achron. It's boasts the most interesting feature in, well, probably any RTS, ever. You'll want to keep reading.
The idea is this: time travel. While you can only travel back by a few minutes, those are enough to change the course of events in the present of your game. Go back a minute and order a tank to cross the map and he'll be appear there in the present. Go back and destroy something in the past, and it'll be removed from the battle you're having in the present.
Time is propagated in "waves", which you can see in your UI. This means that when you make a change in the past you have to wait for that wave that has passed it to catch up with the present before you can see the change. You can, when you are in the past, "fast forward" to the present, so that you can deal with any problems a unit might encounter in its changed history. If you know what events are bound up in a particular wave, you can also work to dodge or undo them. It's an amazingly clever system, and one that blows the roof off the RTS as you and I understand it.
The possibilities for cross-time combat are, I suspect, beyond of my ability to imagine, having played it for such a short time. But you can at least see where your enemy's "attention" is on the time line, so if he's messing about in the past, you can try and stop him. All this is dependent on one key resource: chronoenergy. This stuff regenerates if you're doing things in the present, and reduces as you perform actions in the past. The further back you go, the more expensive actions are. The battle will come in spending your capacity to go back and change things more wisely than your opponent. And yes, there will be single and multiplayer games.
Balance is, presumably, going to make or break this game. And being in a situation where your enemy can go into the past and undo his actions - and yours - means that bringing a game to its conclusion could be tricky indeed. Genuine time paradoxes do seem to be possible - destroying the factory that made your unit before the unit that destroys it was made, for example - but the game should resolve them for you via the time-wave system (see below). More importantly, this is, once you're playing, the kind of thing that videogames should be doing: a really big idea, delivered in practical terms. I can't say it's doing for time what Portal did for space, but it's certainly a fascinating extension of strategy concepts. It's also the best use of time-travel as a mechanical game design system that I can think of. Rather than simply being the rewind/forward function we've seen in any number of action games (or the future-sight of quicksaves, for that matter), it's a system that creates complex tactical potentialities, that you have to work through to resolve by having specific knowledge of the past.
I'm going to go out on a limb and say that while the game is in a crude, early state - it's by an indie studio and is being released in that indie way of "please help us do more" - is visually basic, and might never have the polish your big studio titles boast, you should probably buy it. Hell, you want innovation in games? This is it. Hazardous have made a basic version of the game available now to anyone who ($20) pre-orders. Check out their release calendar for some more information.