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Thursday, March 17, 2011

What makes a good tower defence game?

It’s a reasonably new genre, but tower defence games have experienced a surge of popularity, thanks in no small part to the iPhone, XBLA Indie Games, PSN Minis and DSiWare/ WiiWare.

See, they’re cheap to make. Meaning small teams and indie developers can reasonably quickly turn one over. While we’re now seeing attempts to bring substantial production values into the genre, tower defence games have remained popular as cheap disposable little strategy games.

But with that comes vast disparities in the quality of tower defence games. This is not just restricted to the cheap “$0.99” or free games – some much more expensive tower defence games are terrible, while some of the cheaper ones are awesome experiences. So, the question is: what makes a good tower defence game? Below are five traits that we thing separates the must haves from the leave well alones.

5) Interface

The aesthetics of a tower defence game don’t matter as much as (most) other genres – people are willing to deal with simple, underdone or slightly ugly visuals when the game comes cheap, and music is not an integral part of the tower defence experience, so it’s easy enough to turn off.

However, interface is critical. Nothing is worse than trying to scroll around the map only to find you’ve done something you didn’t mean to, or struggling to pick out the tower you wanted to place on the battlefield amongst a mass of cluttered icons.

We give props to Crystal Defenders in this regard. Units are nice and easy to select and place on the battle field, buttons are of a nice size, and overall it’s a nice, clutter-free interface. You’d expect nothing less from Square Enix, but it’s a good standard for other tower defence developers to emulate.

4) Simplicity

People don’t buy tower defence games for epic stories, sweeping orchestral scores, and thousands of units requiring micromanagement. They’re looking for a basic, no-frills bit of strategy to amuse themselves on the bus or train.

With that in mind, a good tower defence game has a limited range of units, with basic and obvious advantages and disadvantages. Enemy waves shouldn’t have too many different special considerations.

Look at Fieldrunners. It’s a seminal tower defence game, but it only has a handful of towers, a handful of different enemies, and some very basic level designs (in fact you’re essentially building your own level as you go). And for that it’s easy to pick up and play for short bursts, and addictive enough to keep you coming back for more.

3) Difficulty

This is a difficult one for tower defence developers. Tower defence games need to be accessible for the casual audience, but offer enough challenge to stave off boredom from being too simple (see above).

In theory, then, a good tower defence game has an exponentially-increasing difficulty level. Without spiking too dramatically, the early enemy waves should be a cake walk. The later waves should require some serious skill to defeat. The high score leader boards are there to encourage people to try again and beat one more wave.

At the same time, each tower defence “game” should not take too long to complete. 100 levels of steadily-increasing difficulty might sound good, but almost no one is going to play that long.

Taito’s Mikado Defenders balances difficulty better than most. It leans on the side of “difficult” from the outset, but a typical level features fewer waves to deal with, and you’re always going to be competitive with intelligent placement of units.

2) Level variety

Another balancing act, this. For obvious reasons, a good tower defence game features a range of levels to play. The balance comes in offering just enough content to give the impression of variety, while not becoming intimidating with too many options.

Within that level selection needs to be a wide range of different designs and quirks. At no stage should two tower defence levels feel the same to players – that’s just wasted real estate and won’t encourage people to keep playing.

Vector TD does this pretty well. It splits its levels across three difficulty levels, with a small handful of levels in each. Each of those levels are greatly different from others, leading to a varied, interesting experience.

1) Originality

This one is easy, and in fairness to tower defence developers, they generally ‘get’ this. A good tower defence game can’t be generic. It can be simple, but it can’t do something that someone else has already done, because it’ll get ignored pretty quickly.

There are a host of ways to do this – all the games mentioned above offer very different tower defence experiences, even if the underlying mechanics to the games is fundamentally the same.

Whether you go for a crazy science fiction setting, a gritty wild west setting, or abstract art, and whether you go for humour or deadly serious, make your game look and feel different and you should find some kind of audience for your game.

Look at Plants Vs Zombies - such a simple concept, and the game does very little that you can't find in other tower defence games, but with such a fresh presentation and unique concept, it was always going to be a hit for PopCap.

Of course most of these points above apply to just about every genre, and with good reason – they’re fundamental principles of game design. But as something of an apprenticeship for future A-list games designers, tower defence games are prone to occasionally get these basics wrong.

What makes a good tower defence game?
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