So, this game kind of broke my brain.
See, I'm no virgin to strategy games. I know about setting up defenses, harrassing the opponent with attacks, sending waves of units and counteracting other moves while trying to get a suprise attack in. What I needed to learn is how to counteract an attack on a battle that I had already won, while trying to defend a factory while using a group of units from that factory that had not yet been produced. Things get a little more complex.
Achron is a game about time travel. Billed as the only game in the 'meta-time strategy' genre, it involves using time travel to rectify mistakes, to develop counterattacks against battles that had yet to occur, and to create an army of units using just one group and a time portal. There's the basic ability to see into the past, which allows you to change orders, telling units to turn left instead of right, avoiding an ambush that would've destroyed them all, for example. This also involves the need to 'undo' commands, as otherwise you'd still issue the command to that unit ro turn right, even if you had changed the past. This can be an great annoyance at the worst of times, making you wonder why your units are going off in directions that you don't remember ordering them in.
You can also send units back in time using devices called 'chronoporters'. This allows you to create an army of units in the past that could theoretically not have existed there, due to lack of resources, factories, or simply time. This also creates a massive slew of possible strategies and problems, like the classic grandfather paradox of destroying a factory with a unit that factory has yet to create, or a unit stopping itself from being killed.
The important thing to know is that changes in the timestream are not instantaneous; just because you kill a unit in the past does not mean that it ceases to exist in the future. Changes are propagated through 'time waves', waves of change that ripple through the time stream. If a unit dies a minute before the present, that unit will still exist in the present until the time wave from a minute ago hits. This is also how paradoxes are solved, as each time wave starts flipping the state between possibilities, one where the unit that destroyed the factory still exists, and one where the factory exists, but the unit does not.
Does your brain hurt yet? Now try implementing strategies like this while your opponents are doing the same thing, jumping through time to undo changes you've made while you try to counter-act their movements, in the past and future.
All this is done through chronoenergy: anything you do in the past, or the act of chronoporting a unit into the past, requires this energy. This also keeps a limit on how far into the past you can go, which means that after about five minutes or so, things are immutable. Because sure, your plot-important unit might've just died, but as long as you have the energy, this can always be changed.
The game has issues with letting you keep track of what you're doing. While the interface itself is fairly simple to navigate with regards to time travel, there's no way to see what a particular unit's objectives are. So, unless you have a very organized mind, it's nearly impossible to keep track of what is going on in a particular time frame.
Worse than that is that Achron has some serious issues with basic real-time strategy functions. Pathfinding is terrible, especially when units have to navigate around each other. The story is dull and poorly explained, and the cutscenes that separate the battles are long, drawn out, and monotonous. There are numerous interface issues with functions as simple as selecting groups of units. And then there are the units themselves: it's nearly impossible to tell units apart, with identical silhouettes that make any sort of real strategy a chore. Telling apart a tank that can devestate air units and another vehicle that only targets ground opponents requires selecting each, and checking the names of the units themselves. You don't quite realize how much of an issue this is until you play a game that doesn't do it well.
Achron, as a real-time strategy game, is terrible. This is really quite unfortunate, because the time travel mechanics are very well thought-out, with numerous strategies at your beck and call. Being able to manipulate time is something that almost no game has done beyond a cursory plot device or some sort of bullet-time mechanic. Being able to apply strategy to it is just really, really cool. So it's a shame that the rest of the game simply falls apart around it. The real-time strategy mechanics are just not done well, it's as simple as that.
I think Achron is worth a look, but nothing more. It's an amazing experiment that seems to succeed in almost every way, except for the cornerstones are the genre that they're trying to expand from: it's like creating a fighting game in which you can't execute special moves. Anything else you add in may be interesting and unique, but without the core mechanics, it falls flat, just like Achron.