One of the problems with the Galaxian invader type of game is that it must be difficult enough to present a challenge, but easy enough to tempt you back for another go. Zalaga scores well on both accounts.
The program welcomes you with a short tune, and as soon as your ship appears, some very colourful aliens swoop and loop about the screen before joining ranks at the top.
The aliens then dive one by one, Galaxian style, until you have cleared them all from the screen. My only quibble with Zalaga is that the aliens' flight paths become a little too predictable after a while.
Another annoyance is that each time you lose a life, you have to wait rather too long for your ship to be replaced.
Occasionally, one of the larger aliens swoops down and bombards an area of the screen with radiation, and if you're in the right place, and you still have a ship in reserve, it will join you on the screen, blasting away while the Beeb plays some jolly 'let's kill the aliens' music.
When you've finished zapping all of the aliens, there's a Hall of Fame to add your name to - unless you're too busy hitting the return keys to get back into the game.
Zalaga has nothing new to offer the hardened games addict, but what it does is well presented and fun to play.