Hydraulic Empire is a tower defense game with enough new wrinkles to it to make it worthwhile to play, especially at its low price.

There are a dozen towers in the game, including a mud slinger (to slow down enemies), a bomber, a tesla tower, a gattling gun, a netter (to knock down flying enemies), and more. However, you can only take five of these towers with you into a level.

The enemies are fun. They're robots, and while most just simply try to make their way to the exit, others spawn more robots, or repair destroyed robots (so they get back up and start heading for the exit again), or carry smaller robots on their back, or disable your towers, or more.

There are 21 levels. Each level is made up of a hex grid, with start and end points, and possibly some rally points that the enemies also have to visit. Enemies travel on and you build on the hexes, and since enemies can't travel through most of your towers, you can create a circuitous path for them to follow. If you've played Defense Grid (which I'd recommend over this), then it's the same sort of idea.

Each time you complete a level (even if you lose), you earn cogs, which you can use to upgrade your towers. You can grind cogs if you want, or try out extra difficulty settings for extra cogs, but it's not really necessary. I completed the campaign only repeating a few levels.

You can upgrade your towers, both inside and outside the levels. The outside upgrading is sort of confusing, and it isn't explained well in the tutorial. On the "factory" screen (where you upgrade individual towers), you get 14 hexes. On one hex you have to place a tower, but then around it you can place upgrades. That means you can't upgrade all of the towers. You can only pick out like four and give them 2-3 upgrades each.

You build towers using your Keeper. You have to move your Keeper to the hex where you want to build a tower, which can get tricky because your Keeper can also damage enemies and improve the capabilities of nearby towers, so there are usually 2-3 places where you'd like him to be at once. Along with cogs, after each level your Keeper also earns some experience, which leads to levels and upgrade points. So you can improve your Keeper as well as the towers.

The only problem I had with the game is that it stopped recording my progress. It unlocked new levels properly, so I was able to complete the campaign, but it stopped saving my scores, which means it currently doesn't think I've completed most of the levels (and the levels where it did record a score, it recorded the wrong score). So it's not giving me credit for completing the campaign, which is annoying.

But overall, Hydraulic Empire is fun enough. I got it for $2, and it was more than worthwhile at that price.

Hydraulic Empire is a tower defense game with enough new wrinkles to it to make it worthwhile to play, especially at its low price. There are a dozen towers in the game, including a mud slinger (to slow down enemies), a bomber, a tesla tower, a gattling gun, a netter (to knock down flying enemies), and more. However, you can only take five of these towers with you into a level. The enemies are fun. They're robots, and while most just simply try to make their way to the exit, others spawn more robots, or repair destroyed robots (so they get back up and start heading for the exit again), or carry smaller robots on their back, or disable your towers, or more. There are 21 levels. Each level is made up of a hex grid, with start and end points, and possibly some rally points that the enemies also have to visit. Enemies travel on and you build on the hexes, and since enemies can't travel through most of your towers, you can create a circuitous path for them to follow. If you've played Defense Grid (which I'd recommend over this), then it's the same sort of idea. Each time you complete a level (even if you lose), you earn cogs, which you can use to upgrade your towers. You can grind cogs if you want, or try out extra difficulty settings for extra cogs, but it's not really necessary. I completed the campaign only repeating a few levels. You can upgrade your towers, both inside and outside the levels. The outside upgrading is sort of confusing, and it isn't explained well in the tutorial. On the "factory" screen (where you upgrade individual towers), you get 14 hexes. On one hex you have to place a tower, but then around it you can place upgrades. That means you can't upgrade all of the towers. You can only pick out like four and give them 2-3 upgrades each. You build towers using your Keeper. You have to move your Keeper to the hex where you want to build a tower, which can get tricky because your Keeper can also damage enemies and improve the capabilities of nearby towers, so there are usually 2-3 places where you'd like him to be at once. Along with cogs, after each level your Keeper also earns some experience, which leads to levels and upgrade points. So you can improve your Keeper as well as the towers. The only problem I had with the game is that it stopped recording my progress. It unlocked new levels properly, so I was able to complete the campaign, but it stopped saving my scores, which means it currently doesn't think I've completed most of the levels (and the levels where it did record a score, it recorded the wrong score). So it's not giving me credit for completing the campaign, which is annoying. But overall, Hydraulic Empire is fun enough. I got it for $2, and it was more than worthwhile at that price.