[Sailor Steve]

As was said above, each has something different to offer and something none of the others has. SH5 with the modern mods is a visual feast, and many people love it above the others. So why play anything else, especially when the others look their age?

Unfortunately SH5 still only allows for a variant of a Type VII u-boat, and probably always will. If that's not what you play for, then the game is well worth it.

Only SH4 gives you an opportunity to command an American fleet boat in the 'Silent Service'. That said, the complete SH4 1.5 also lets you run a u-boat and Operation Monsun lets you do it throughout the entire war, a la SH3. SH4 also has some functions that neither the older or newer versions has, including the most realistic crew management system.

SH3 is still the only version that offers "realistic" eye-candy, such as working locks in the canals and harbors that had them (via LSH3, but available as a separate add-on for GWX), a tool (SH3 Commander) that gives realistic names, tonnages, cargoes and crew numbers to the ships you sink. There are also a wealth of other mods that let you tailor the game to your liking.

Again, it's all up to what you want from the game.