An interesting origin of the Metal Gear series
In this game many elements from the more popular Metal Gear Solid could be seen: nearly identical list of weapons, similar (but much less verbose) storyline, and items (as in the ever-present cigs).
It is slightly repetitive and at times frustrating - I'd even argue it's harder than its third installment due to its basic strategies. The storyline, as mentioned, is very minimized - the characters responding to codec frequencies merely repeat themselves; whereas in MGS the storyline is very much in the forefront, with vast backgrounds created for most characters in the game that parallel real-life political issues, Metal Gear is certainly a contrast to that, even for games as old (although this was the first game I've played on the MSX, and I'm not even sure the system was adequately powerful for long storylines).
The Bottom Line
It was a promising beginning in establishing a whole genre.