Spartan Assault sees Halo move into your pocket, as the popular gaming franchise makes its move on to Windows and away from the console.

We got our hands on an early build of Halo: Spartan Assault before its release, playing the game on Windows Phone 8 on the Nokia Lumia 928, as well as on Windows 8 on the Surface Pro tablet.

Halo: Spartan Assault is an entirely new Halo game, built from scratch for mobile devices: it isn't a port or a reworking of an existing console game. As such it segues into the existing Halo universe, while not being entirely dependent on the happenings of earlier games. 

As a representative of 343 Industries told us, the game has been designed to appeal to Halo fans and the casual mobile gamer alike. That means that while the control mechanisms make this game easy to pick up and play, if you've spent any time with previous Halo games, you'll recognise characters, and the missions will have a wider context in terms of the Halo universe story.

There's a twist, however, when it comes to the story. To ensure that Halo: Spartan Assault doesn't railroad into the middle of Halo lore, 343 Industries says that Spartan Assault is actually a simulation, running on board Infinity for Spartans to train. A convenient caveat, but also an effective mechanism.

This arrangement means that Spartan Assault can give you missions that have Halo context, but can survive in isolation. The central character of Spartan Assault at launch is Sarah Palmer and much of what you play relates to her character's story.

The story is brought to life with cinematics, which from the example we were shown look and sound fantastic on a mobile device, so you're not just pitched into an abstract mission, you're told why this mission is of significance. Before you start a level, you have a brief synopsis page as well as a tactical map, so it's pretty easy to determine what you have to do.

Story, context and narrative techniques aside, many will be more interested in getting into the action. Many mobile games are thwarted by the same control issues. As such, 343 Industries' Dan Ayoub told us that they'd thrown out "about a dozen" control mechanisms before settling on the dual thumb controls.

However, rather than having two static locations for those controls, they cater for creep, where your thumb slips off to a different location on the surface of the display. Rather than losing control, the controls simply moves with you.

In practice this seems to work and from the 30 minutes or so of playtime that we had, we found slippage wasn't a problem. Occasionally we'd find we'd slipped to the edge of the device we were playing on, but generally speaking, the controls work.

Those two "thumb" controls give you directional movement for your character or vehicle on the left, while the right stick handles the direction of fire. This is a top-down shooter, so the controls work well: as the enemy moves around you, you can move your character in any direction the environment allows, as well as fire in any direction.

Your skills amount to more than just blasting away with your primary weapon however. As you'd expect, you can carry a secondary weapon, as well as grenades and you have other skills too. There are some weapons and skills unique to Spartan Assault that you won't have seen elsewhere in Halo.

You get the chance to change your loadout before you start a mission, as well as being able to switch to weapons you find on the battlefield, as well as jack vehicles, as you'd expect. To begin with only ground vehicles are supported, and our brief time in a Wraith proved fun.

There's a lot going on too. Thankfully there's plenty of detail and the rich graphics of the Surface Pro soon had us hooked. The Windows Phone 8 build we saw was earlier in development, so missing some graphical elements, but still looked great. We also had it confirmed by 343i executive producer Dan Ayoub that Halo Spartan Assault will run on all Windows Phone 8 devices, from the entry-level to the high-end.

There's an achievement system and medals to collect, as well as challenges to keep you playing and one of the features we really like the sound of is cross-device syncing. To keep Halo: Spartan Assault on point across your devices, the game will support auto cloud saves, so you can play a little on your Windows PC, then resume on your Windows Phone 8 once you leave the house.

We've not seen this in action, and the build we were playing didn't have any support for incremental saves: each time we died, we restarted the mission. And die we did, because Halo: Spartan Assault is no pushover. It has been designed to play as a AAA title and it left us wanting more. Although it's easy enough to pick up and play, it feels like there's more to the game than just blasting your way through.

As a first impression, that's really important to us. Not only because this game is flying the flag for a huge franchise, but also because mobile gaming is getting more and more impressive, offering more depth, better graphics and an experience that's worth the investment of your time.

Halo: Spartan Assault will be launching in July 2013, pricing still to be confirmed. It will, however, be Windows only.