New enemies join the fray, such as the (frantic, mutated humans) and the Zealot (a hard-hitting, shielded knight).
Serious Sam 4 introduces the Legion System, a rendering technology capable of putting tens of thousands of active enemies on screen simultaneously. This creates battlefield scenarios of an unprecedented scale, particularly during the game's climactic final battles. A Massive Arsenal
The GOG community has generally received Serious Sam 4 positively, appreciating the DRM-free nature of the release. However, some users have noted that GOG's update process can lag behind Steam. For instance, a GOG forum post from around the time of version 1.06 noted that the “changelog copied over from Steam (because GOG didn't bother or didn't manage to update the changelog...)”. This is a minor but recurring critique of the GOG platform.