At this year's Leipzig Games Convention eager Halo fans were treated to one of the first publicly playable multiplayer Halo 3 events. Meanwhile, far from the madding crowds, a new single-player level was demonstrated to an eager huddle of games press in a heavily guarded private booth.

The level in question was named Tsavo Highway, set on earth, and had a heavy vehicular emphasis. The mission required Master Chief to make his way to a pair of fellow marines pinned down in a tiny battlement. After arriving at the checkpoint he joined the soldiers in defeating waves of Brutes with a selection of new weaponry.

Immediately it was obvious that the visuals in the single-player campaign are far superior to those seen in the multiplayer Beta. Tsavo Highway is immense and expansive, requiring some huge drives that largely had to be skipped to shorten the demo time.

Once reaching the point of the level's climatic shootout, it was clear that new technologies and abilities such as the Bubble Shield are now readily used by the NPCs. The game's AI has also been shaken up, with an obvious increase in the levels of aggression your enemies apply across the difficulty levels.

However, the Easy and Normal difficulty settings of the landmark shooter have now been toned down, apparently in an attempt to tempt any gamers still not lured in by Halo's ample charms. Long-time fans needn't worry though, as the Heroic and Legendary settings have been intensified to add further challenge.

Viewing the Tsavo level it was also clear that the new division of Brutes into Chiefs and standard warriors has a noticeable effect on the gameplay. Chief Brutes will spend their time hovering at the back of a skirmish, supposedly giving orders and certainly taking more considered shots at you and your allies. Meanwhile the standard Brutes are more familiar and unorganised, though their increased hostility is not to be underestimated.

Several new weapons were also seen in use in the demonstration, and in many cases it was the NPCs that demonstrated their use with the most prowess. At the most basic end of the spectrum was the flash flare, a new projectile that temporarily blinds without doing any damage, suggesting a specific use in an as yet undisclosed mission. There's also a powerful new missile gun in the form of the devastating Fuel Rod; a compact assault shotgun called the Mauler, that appeared very hard to resist using at close range; and a flame thrower that now admits a napalm-based incendiary that stays flaming for sometime after you have moved on.

The melee-based Gravity Hammer, one of the most explicit of the new additions to the weapon set, looks somewhat easier to use and more functional that many first expected, ending fears that it may be a pointless and lumbering war hammer totally out of place in the Halo universe. Finally we were treated to the new napalm-based Fire Grenade, which joins its Frag, Brute and Plasma cousins on the role call of Halo's handheld explosives.

After the conclusion of the Tsavo Highway level, our endlessly enthusiastic host treated us to a demonstration of the curious Forge mode, which is best described as a tool for simultaneous level editing and multiplayer matches. Of course this concept sounds a little ridiculous, but exploring its features reveals it to be a unique new direction for user generated content and fragging with friends.

The editing aspects of Forge are not particularly revolutionary, allowing the player to change everything apart from the geometry and buildings of the game's levels. This means vehicles and weapons and crates can be spawned all over each map, allowing for bases to be moved for example, or even a complete tactical reworking by subtly changing the firepower on offer.

Of course you can redesign levels in this way in peace, but the real tactical challenge comes when you and a team work together to re-spawn weaponry and redesign areas as a battle rages on. The most obvious tactic is to divide your team into those fighting and those providing back-up through the editing tools, but watching a forge battle commence reveals far more cunning strategies.

The new Forge mode should spice up multiplayer battles

Take for example, the player who places one half of a teleporter outside their base before hovering above the map with the other end, meaning he can drop off team mates wherever they desire. There's even the more Neanderthal technique of simply dropping scenery on enemy heads. Either way, these rather unorthodox approaches to FPS tactics show how Forge mode reinvents the concrete world of the FPS as a flexible and liquid place where imagination can be as powerful as the most destructive Covenant weapons.

My personal tour of Forge mode also revealed a rare sight of the new hover tank known as the Prowler. This 4-player capable battle craft is very similar to the Brute Chopper - itself a version of the Ghost. Armed to the hilt with three gun turrets, it gives a tantalising glimpse of what other moving fortresses will join the now legendary Warthog.

Finally, Forge also allows for players to upload and download the best of the user generated maps and videos in the new 'Bungie Recommends' service; a kind of YouTube for Halo fans that allows less creative players to enjoy the most popular Forge levels, and more imaginative players to show off their creations.

Bungie still has a great deal of Halo 3 hidden in its vast wizard's sleeves, and fans will expect the magic to keep on coming. Based on the output so far, it looks like they have nothing to worry about, but following in the footsteps of such mighty forefathers means the volume of expectation cannot be underestimated.