This is a fantastic version of Space Invaders. Pushing the ZX81 and getting very smooth, very playable large moving graphics. Has all the playablility of the original arcade. Far far better than the old ascii versions that we had to live with in the 80s. Definitely a 5 out of 5. Please purchase the cassette version, even if you download the free digital version. Help keep software production for this awesome wee machine alive. Well worth 5 quid!