Doom Eternal's main campaign takes about 14½ hours to complete when focusing on the main objectives. For players aiming to experience everything and achieve 100% completion, the playtime extends to around 28 to 28½ hours. This includes finding all collectibles and completing all challenges

. The game length can vary depending on difficulty and playstyle. Skilled players can finish the game faster, sometimes in as little as 4-6 hours on speed runs or Ultra-Nightmare mode, while casual players or those exploring thoroughly may take longer. Playing on harder difficulties and collecting all secrets can push the time closer to 20 hours or more

. Including the downloadable content (DLC) expansions, the total time can reach approximately 25-30 hours to complete all achievements and content

. In summary:

• Main campaign (main objectives): ~14½ hours
• Full completion (all secrets, challenges): ~28-28½ hours
• Including DLC and achievements: ~25-30 hours
• Speedruns or very skilled playthroughs: 4-6 hours

This makes Doom Eternal a moderately lengthy first-person shooter with a substantial amount of content for completionists and casual players alike