It sometimes runs on video game logic (for example, some pretty bad injuries can be healed instantly with the right equipment while others can't) and is bloodier than I would have expected. I'd say you don't need to be too familiar with the games as the show tells its own story. It has quite a few references to tropes from the games but even if you don't get the reference, it should still be enjoyable.

In general don't trust sensationalist reviews that call it the best or worst show of the year.