Just as the Daleks' original galactic domination plan was defeated by stairs, so there's a class of tower defence enemies that suffer from an equivalent issue: they're limited to pre-set paths.
Good news for us defenders, but it means that - in contrast with games like Fieldrunners - much of Com2uS's Tower Defense: Lost Earth is about finding the fine balance between tower and enemy types, rather than worrying about freeform unit placement and enemy re-routing.What's my name?
As an aside, you might be wondering why other tower defence games on the App Store are labelled 'TD', while Lost Earth manages to get full Tower Defense status. That's because Com2uS has the US copyright for the term 'tower defense', ensuring the competition is limited to the abbreviation.
The publisher knew there would be a lot of eyes on Lost Earth, and this is reflected in the high quality of its colourful, sprite-based graphics, its scale, and the amount of time that's been spent polishing the gameplay balance.
Lost Earth appeals across the full range of players, too. Newbies playing on Easy are provided with a reasonable difficulty curve, and can have fun in early levels placing loads of towers and seeing plenty of explosions.
The additional options - Normal and Hard - provide much more challenging experiences for TD generals.Incoming
The game is well-paced in terms of the way it introduces the nine towers and ten enemy types. When combined with the pre-set routes to your base, this means there's a well-defined range of options that both allow you to use your favourite towers and provide some structure at the same time, forcing you to learn how best to destroy certain enemy types.
These consist of the usual mix of slow but hard to destroy, and fast but fragile units. The most interesting are slow Spawners, which, when destroyed, split to reveal three fast tumblers. These speed along paths en masse to overwhelm defences, but are slowed by corners, providing a brief killing zone.
An equivalent for towers are the laser units. When positioned along a path, they will fire through all units on that track, zapping health from all of them. Lasers are highly effective, if expensive, and look cool.Defence spending
Lost Earth is careful not to confuse players. Levels start with the familiar placement of cheap, quick firing towers and then expand to offer you more strategic and personal options.
Maybe you prefer homing missiles or area-kill grenade launchers? Alternatively, maybe you'd rather bulk up on the cheap but massive-ranged scout towers?
Non-lethal support options include slow-down towers and credit card-style generators to boost your resources ahead of time.
Of course, budget management, in terms of whether to build more towers or upgrade what you have, is another element of your decision-making. The higher difficulty you decide to play on, the more razor-edged those decisions need to be.Drop da bomb
Providing leeway are the smartbombs you get to use once per mission. These are pre-selected for each level and include bomber strikes, a single nuclear bomb, poison gas, and changing gravity to slow down enemies. Sometimes - often - they mean the difference between success and failure.
Further variation is generated in the boss levels, which introduce one-off super enemies to kill. As you progress through the game, some levels require you to destroy environmental obstacles so you can better place your towers in strategic locations.
This sort of layering keeps the game fresh - something enhanced by mission types such as Survival (wave or timed) or gaining a certain amount of resources. The game's achievements encourage bravery, too: one suggests you manually group at least a quarter of the waves together to make your task even more difficult.
And as you complete the 40 Campaign levels, you'll unlock additional levels in the separate Mission mode. Interestingly, these take the Fieldrunners freeform approach in letting you use your towers to create paths for the enemies. They also link into global leaderboards, which use Game Center and Com2uS's own social hub network.
All-in, Tower Defense: Lost Earth provides a sizeable package for anyone interested in tower defence games. It doesn't do much that's novel, but in terms of sheer polish - graphical, audio, UI - and value for money, it's very hard to defeat.