The tower defense genre is one of the biggest success stories of gaming’s last decade. Numerous indie developers made a name for themselves with variations on the theme. Some, like Plants vs. Zombies and Kingdom Rush, still appear on best-seller lists of iOS and Android years after their debut.

With that said, the genre isn’t as vibrant today as it was two or three years ago. Gamers want something different, and some are turning to tower offense instead. These games let players take an offensive role and often combine action packed gameplay with puzzle-solving and strategy. Though still a young sub-genre, there are already some excellent choices available.

Anomaly: Warzone Earth / Anomaly Korea / Anomaly 2

The Anomaly franchise is the game that started it all. Originally released in early 2011 for Windows, and then ported to iOS later the same year, Anomaly: Warzone Earth won multiple awards including Game Of The Year Runner-up (from Apple) and best iOS strategy game (from Touchgen).

You don’t have to play long to see why this title was such a hit. Besides its unique concept, Anomaly offers beautiful graphics, decent voice acting (for an indie title, at least) and a campaign that lasts about ten to fifteen hours. The difficulty curve is well-tuned, too; early missions are simple, but later ones get quite tricky. There’s a wide variety of units and the commander "hero" unit the player controls improves game’s pace and demands the player’s attention.

Two new additions to the franchise, Anomaly Korea and Anomaly 2, have been released. They carry on the original’s approach while adding new challenges, new units and new powers. Anomaly 2 also adds competitive multiplayer, with one side playing offense and the other defense.

All three games are available on PC, Android, iOS and even BlackBerry, though pricing varies by platform.

Gratuitous Tank Battles ($9.99, PC-only)

Developed by a one-man team, Gratuitous Tank Battles is a strangely awesome game that puts tower defense, offense, real-time strategy and unit customization in a blender. Initially it appears to be a rather basic tower defense title in which you set up towers to defeat enemy tanks, but that impression disappears the moment you realize your enemies are firing back.

This small detail completely changes how the game is played, turning it from tower defense into real-time strategy against an opponent that follows pre-defined paths. Layered on top of that is extensive unit customization that lets you change everything about the units you deploy.

And, as if that’s not enough, there’s the offensive element; you can play every map as either defender or attacker. Oh, and did I mention that the deviously clever AI adapts to the way you customize your units, making a one-size-fits-all solution impossible? It will even use your own custom units against you!

If this all sounds a little overwhelming, that's because it is. This is a difficult game to come to grips with, but once you do, you’ll find that it offers the kind of variety that most strategy games simply can’t match. You can outfit your units in countless ways and, because the AI adapts, you must constantly evolve your strategy. There’s even a competitive multiplayer mode for players who get tired of competing with the computer.

Gratuitous Tank Battles is $9.99 on PC only. There’s also an expansion, The Western Front, available for $5.99.

Royal Revolt (Free)

Royal Revolt is a cute little title that puts you in the shoes of a prince trying to take back his kingdom. To do this you must capture a variety of castles, and that means marching on them and their defenders.

This game is really a blend of tower offense and MOBA (multiplayer online battle arena). You have a hero, your prince, who you control directly, and also a variety of other units that you deploy but don’t control. The castle you’re assaulting has no hero, but it does have units as well as static defenses like towers and traps.

Unlike the previous two titles, Royal Revolt is almost entirely about action. Victory hinges on using the right attacks at the right time, avoiding heavy-hitting defenses, and coordinating with your troops. Thankfully, the action on offer here is pretty good – anyone who has played a MOBA or an action-RPG will feel right at home.

This game is free-to-play with in-app purchases on Android and iOS. The endless prompts to connect your social networks and spend real-money can become annoying, but this is otherwise a great pick for mobile gamers.

Eden to Green (Free)

Released in 2012 alongside the Tegra 3, Eden to Green was used by Nvidia to show off the 3D graphics power of its new mobile chip. Most people who saw it deemed it a rip-off of Plants vs. Zombies, and promptly ignored it.

That judgment isn't entirely correct, as the game is actually a turn-based tower strategy title that sees the player fighting off evil machines. You do this by placing planets on the map, each of which has various attacks or abilities that can be used within a certain radius. Winning requires careful consideration over unit placement to make sure you can execute what you need on your next move, and enough foresight to be able to see your chosen strategy through the next few turns.

The graphics, originally a highlight, no longer look outstanding but they hold up pretty well considering the game's age. And since the game has been taken over by Zynga, it’s free to play (with in-app purchases, of course). Eden to Green is available free on Android and iOS.

Any Others?

There are a few other titles in this genre, but these are  widely regarded as being the most fun. With the exception of Eden, all of these games have done well, but it remains to be seen if they’ll spur a lasting trend or are just a fad.

We'd love to hear what you think about tower offense, as well as any of your favourite games – so sound off in the comments!