What a piece of work is a graphic adventure on the Beeb. Not simply how infinite its facilities but how colourful its artwork, how endearing its playability, how easy its concept and how taxing its puzzles. These are the questions asked ever since Citadel-style gaming was born and it is what might be termed the "inadequacies" of each particular graphic adventure that determine their own appropriate subcategories. There are quite a range of titles to choose from; successive releases all attempting to offer improvements or "differences" which may improve upon the elements shared by all.

The classic graphic adventure, to my mind, is Palace Of Magic. One of the earliest (and most hyped) Superior releases, there we find all the elements that can be used as "building blocks". There are typically two levels on a screen viewed from the side and they are connected by ladders, patrolled by nasties moving in set patterns, littered with keys and power capsules and the way out left or right of each screen leads to another - hence the player will quickly find himself making a map to get from A to B in the fastest possible time. All foes - baddies, spikes, etc - must be negotiated by jumping and any contact with them drains an energy bar. Its graphics are fantastic, its execution perfect, its puzzles intriguing and, best of all, if you are losing energy very quickly, saviour code whips you back to the point at which you entered!

The latest platformer to hit the PD circuit is Moonbase Beta, a 100% machine code arcade expedition in space written in 1992 (some six years after Palace Of Magic) in which the palace is switched to a moonbase but which otherwise tries to stick close to the tried, tested and loved elements of the groundbreakers. Of course, applauding a product for being like something else isn't always an accolade. However, in the realm of graphic adventures, authors diverging from the classical elements described above fall to be described very disadvantageously. For example, despite excellent graphics, Spycat ruined a promising scenario with an overcomplicated pick up/use/drop object routine. Peter Scott's games where nasties collide with one another, the hero can fire a gun and the action speeds along like greased lightning never keep me at the keyboard long enough to solve the puzzles. Likewise, games missing the energy-saving procedure (The Golden Figurine), allowing you to be stranded indefinitely in a pit on account of one lapse of concentration (Citadel) or just being too darn slow executing (Baron) have fallen under the "too fiddly" filer.

Having said that, the latest pretender to the graphic adventure crown appears to owe more than a passing nod to some of those which precede it. Done in Mode 5, but utilising the extra colours of the BBC via machine code, its spacesuited Agent uses the same taylor as the hero of ASL's Thunderstruck and the scrolling door entrances are faintly reminiscent of Spycat, while being slightly better. The code has no problem plotting Special Agent Sid in front of a "garage style" door (decorated with computer terminals and arrows) and raising it portcullis-style as per Spycat - but it then goes on to lower it in front of Sid so he, in effect, disappears behind it. Nice touch.

The rendering of the graphics is quite superb, with a multitude of sprites packed into the BBC's memory and laid out in very well-ordered rooms which are displayed slideshow-style during the title sequence before you begin. This too is a familiar element in all of the best (and some of the worst) graphic adventures. As the game is disc-based, there is even room for on-screen instructions in the form of a scrolly message plus customised font and loading screen featuring a planetrise plus foreground sprites. The effect is belittled a bit by the odd spelling and grammatical mistake but not seriously.

Movement is via the standardised key layout of ZX*? with the extra keys P for pick up, U for use and, oddly, C for switch between the two objects carried. These extra keys can be a tad confusing if you're used to the type of jaunt where you simply cycle through objects while standing on 'bases' (always dropping one and keeping hold of two) and they 'use' themselves if they are in the right location. You first need to search for a spring in this game to be able to jump but just picking it up is not enough. You must select it with C and use it with U. Although it's nowhere near as 'fiddly' as that of Spycat, it is awkward and it would be much simpler if such an item immediately became 'part' of the suit on being touched.

From this excrutiatingly simple combination of keypresses (hinted at in the opening scroller), the puzzles move upwards in complexity - but all are perfectly solvable with thought. As in Omega Orb and Network, you can also log into computer terminals (after you've brought the mainframe on line) to progress in the game. The instructions also mention some doors are disguised as walls.

The only real drawback with this title is that it is all too easy to make a mistake and see your energy bar drain all the way to zero. On the electrified floors, live wires and safe wires look identical and the impressively-designed aliens rebound off one another and zip toward Sid to zap precious energy away in record time, particularly on that first game. As in many of those graphic adventures in the fiddly file, the lack of saviour code renders the death (disintegration) far too frustrating for the player to want to continue playing for long.

The bottom line is that Moonbase Beta feels fashionable and plays professionally but, like many others, cannot sustain interest. If you like the genre of the graphic adventure, this is one of the best titles in it and it is possible to get quite far into it with perseverance. The energy bar (as opposed to a lives' system, see Jet Set Willy) and some ingenious inclusions make it one of the most exceptional PD efforts around. Unfortunately, the tragedy is that the little omission of saviour code takes away such a lot of playability. Stick this in and it could almost have been another Ricochet!

Dave E