Antonym: "repetitive"

Ever-changing

adjective: ever-changing; adjective: everchanging

constantly changing or developing. the key is adapting to the ever-changing conditions

--Google search define operation (ever-changing)

The game is dynamic

I prefer 'dynamic'

I would suggest:

Enduring

e.g. A book of enduring interest

Oxford dictionary: lasting for a long time e.g. What is the reason for the game's enduring appeal?

A similar (may be less suitable) option may be

kaleidoscopic

Cambridge dictionary

quickly changing from one thing to another

Freedictionary.com

continually shifting or rapidly changing; having a marked tendency to change e.g. a kaleidoscopic and fractured view of Los Angeles

“Unpredictable” comes pretty close, I think.

Unpredictability can be seen as a negative, especially by those who thrive on certainty, i.e., repetitiveness, but as long you’re not referring to its tendency to unpredictably crash or freeze, I think an unpredictable game would be considered dynamic and ever-changing (2 more suggestions).

If you're not dead-set against phrases, you could use the following to describe the game:

This game never gets old.

If you want to highlight the fact that there is always something new to do in it, you could use:

This game is inventive.

From oxford:

inventive: Having the ability to create or design new things or to think originally