This game was one of the best of its generation, with a depth and replay value far beyond many other productions. You are basically a pirate/privateer/trader in the Caribbean and the goal of the game is to retire rich, influential, and married. There are also abducted relatives of yours you are supposed to track down. The length of the game is primarily determined by the character's health, e.g. if you get wounded in battle too often, you will not be able to sustain a very long career.
Gameplay consists of setting out to sea, plundering towns and looting ships, also trading, finding the occasional hidden treasure, etc. Every few years, you divide up the plunder (kill off some of your own men before that in battle, this will increase their happiness and share of the loot), then start another expedition. The length of each expedition depends on the morale of the crew (so frequently check morale by pressing fire or space, then select "party status"). At some point they will mutiny if you go on too long without dividing up the plunder.
Unlike other famous Sid Meier games like Railroad Tycoon and Civilization which were strongly influenced by—or one might even say ripped off—existing board games designed by Francis Tresham (1829/1830 and Civilization, respectively, both published by Avalon Hill in the US), Pirates! was a relatively novel concept for its time. (While there is another board game by Tresham called Spanish Main, it has little resemblance to Pirates!.) Notable earlier computer games that feature some elements seen in Pirates! and could have served as partial inspirations include Oregon Trail (1971), Taipan! (1982; ported to the CPC by Ocean as Tai-Pan in 1986), Broadsides (1983), The Seven Cities of Gold (1984), and The Wild Bunch (1985, CPC-only). The Seven Cities of Gold in particular is an influence on Pirates! Meier himself has acknowledged in interviews.
Perhaps the main problem of Pirates! was that its arcade sequences were a mixed bag: Battles at sea (both ship-to-ship and the captains dueling) were fun, but land battles were rather boring. Also, with land battles, the outcome seemed to be largely predetermined by the numbers on each side, so the exhilarating against-the-odds quality of sea battles—defeating a large, heavily armed galleon with a fast sloop and a much smaller crew—was largely absent with land battles. I.e., if you are outgunned and outnumbered in a land battle you will probably lose. The 2004 (and later) versions did not really solve this problem with land battles at all and in fact even added more boring arcade sequences like dancing and sneaking into/out of town.
Still, despite of its flaws, Pirates! with its groundbreaking, highly polished mix of action-adventure, RPG, and simulation is considered a major gaming classic and the CPC version does not disappoint either, at least in terms of playability (graphics are another matter).
Some new updated versions were made too: "Pirates! Gold" (with VGA colours on PC) and a modern PC "Sid Meier's Pirates!" 3D version in 2004.
Pirates! includes a lot of Graphics (Mode 0) and music. The game is notable for being one of the (too) rare 6128 specific game: only disk version and 128KB RAM were supported. In theory, 464 (+ disk drive) and 664 with Extra Ram upgrade should work. (maybe not ?)
This port of Pirates! is also notable for its underlying structure being written in Locomotive BASIC, augmented with machine code routines for graphics, audio, and the arcade portions of the game. Presumably this is largely the same BASIC code as in the C64 version, although on the C64 it is apparently much harder to access than on the CPC (where the files are not hidden in the catalog and only protected by the standard ",p" BASIC protected mode).
Despite it's ultimate awesomeness, the Amstrad CPC port was a bit slow and graphics could have been a bit better. They were somewhat obvious as a C64 port in that respect.
As a result, most graphics, while not bad, didn't make the best use of the specific CPC palette and most graphics look like having the C64 colour attribute—no more than 4 colours per characters and some bad ink choices.