When the combined forces of evil are encircling your Space Marine troops as they shelter behind thin cover with their bolters poised to fire, there's no time to dither about your tactics or hesitate over your orders. You have to act.

And if you're playing Warhammer 40,000: Dawn of War II - Chaos Rising, with OnLive's supposedly touchscreen-friendly 'gesture' controls, the life expectancy of those brave soldiers is roughly the same as giraffe in the trenches of World War I.

It's just about possible to play Relic's game-changing real-time strategy title with the tap-to-attack system, but there won't be a moment where you won't yearn for the ultra reliable mouse clicks of the original PC version.

Of Orks and Space Marines

First launched in 2009, Dawn of War II - the original game and its expansion Chaos Rising are included in the OnLive version - managed to transform the traditional RTS into something more immediately satisfying.

Disregarding the Dune II legacy of base-building and resource-management, the game focuses instead on hands-on management of squads of soldiers.

Using each unit's distinct weapons and skill sets (from cloaked stealth attacks to jump packs) you constantly need to outflank and outsmart the enemy, as well as find sturdy cover to recuperate behind.

You can also level-up your Commander and squads, RPG-style, giving you access to new powers and specialisations.

Double tapped out

Of course, such daring moves require some finesse to accomplish - especially with no mid-mission saving.

On PC, Dawn of War II's combination of mouse clicks and smart keyboard shortcuts (individual units are automatically assigned hot keys, for example, as are special powers) are reliably intuitive.

OnLive's gesture controls attempt to replicate the mouse control with a straightforward double-tap system, whereby you indicate where you want you units to move with one tap and then use a second finger to tap a confirmation. Meanwhile, you can gather units together by drawing a square around them.

The problem is that using OnLive over wi-fi is a spotty experience - even sitting a couple feet from the router - and there's a noticeable lag between your input and the game's response.

This, combined with regular moments where the game doesn't respond at all or misinterprets your orders (often deselecting units at the same time), can prove disastrous in the heat of battle.

In fact, dialling the difficulty back to Beginner is seemingly the only way to handle particularly fraught moments - like tackling the regular bullet-sponge bosses.

Chaos theory

If you're prepared to wrestle with the controls, you own a tablet with a screen big enough to take in the action, and you know how to tweak your wi-fi channels to get a strong, clear signal, there's a lot of game to enjoy in Dawn of War II.

You get the original 12-hour or so campaign and the standalone follow up, Chaos Rising, which features a more apocalyptic storyline - even if the gameplay remains largely untouched. Sadly, the two multiplayer modes (Last Stand and standard PvP) were ghost towns whenever we tried to test them.

Three years on, Dawn of War II remains an RTS benchmark that's an essential play for Warhammer devotees. But even if you're a diehard fan we recommend that you give the 30 minute OnLive trial a go first to see if you can get to grips with the controls.