After I purchased Sol Survivor, via steam, I quickly found very few people play the multiplayer. Because of this single player is most likely where the bulk of your time will get spent. Upon starting a single player mission you choose a commander, which dictates what type of attacks and turrets you can use, and after choosing your commander you set up turrets to defend against waves of enemy soldiers. Unlike most turret defense games these enemies follow a set path as they attempt to destroy your base, so you can't use turrets to tunnel them. The first few waves are pretty lame, for 5 or so rounds just about any moron could defend against the weaklings being thrown at you. Yet by the time the last round comes around you are frantically laying and upgrading turrets, launching waves of missiles and unleashing vulgar comments as you watch enemy units get into you base despite your best efforts. Assuming you finish with less then 20 units reaching your base you get access to a few more units, commanders, or attacks and move on to the next mission. Overall single players takes roughly 20-40 hours depending on which difficulty setting you play on, and whether or not you try to get through each level without letting a single unit through.
After completing the single player campaign you may want to try out the co-op mode, my advice is to just skip it. The co-op mode has one player playing as backup, which means they can only use missiles, and another setting up turrets. I don't know why Co-op was set up this way, but it really sucks because the guy playing backup just sits there watching for most of the game.
Luckily the multiplayer is nothing like the co-op. Just like single player you choose a commander, and defend against waves of enemies. You have the option to play against each other or to play on the same team. Either way the result is the same a lot of fun, I guarantee any fan of the rts genre will end up having at least a little fun.
This game does have a few issues however. To begin with there are no resources out there for the modding community. I feel any type of rts game needs at least a map editor for gamers, also given the fact that this is an indie game a map editor could really help increase the amount of content out there without increasing the production cost. Secondly I have been unable to find any type of multiplayer survival mode, which means once you can beat 27 or so waves of enemies on insane there is not much left to do. And to top it all off you can only play with three other people at a time. Hopefully in the future at least one of this issues will be amended. But even if it isn't this game is defiantly worth the 10 bucks.