The 20 year old internet protocols, for Halo CE, haven't been updated (legacy Bungie code), so game still uses "lockstep" for Co-Op. This means there is really bad input lag (1-2 seconds) when joining another player as host, as everything needs to "sync to the house" first. The same issue occurs for the other player if they join you as host.

It is unplayable like this, and really should've been fixed before releasing. The issue is widely discussed on the internet and here in Steam's discussion threads for the game. The issue is with the game's outdated code (written back in the days of dial-up), and not anything to do with my or friends' connections -- I have 200meg, and myself and those same friends get 10-20ms ping when playing other games together.

See for reference:
https://steamproxy.net/app/976730/discussions/0/2146469724200258510/
https://www.reddit.com/r/halo/comments/e6tlk7/mcc_pc_coop_input_lag_potential_fix/

If you plan to play single player, game is fine (the reskin is underwhelming at best, though). However, if online Co-Op is your aim, either look elsewhere or hold out for the unlikely event this gets fixed. I wish I'd known about this glaring issue before buying -- it makes the game unplayable in Co-Op (which is a shame, as I really do love the game, and was looking forward to replaying it with Steam friends...).

The devs trying to make the game pretty rather than playable in Co-Op was a bewildering development choice...

The 20 year old internet protocols, for Halo CE, haven't been updated (legacy Bungie code), so game still uses "lockstep" for Co-Op. This means there is really bad input lag (1-2 seconds) when joining another player as host, as everything needs to "sync to the house" first. The same issue occurs for the other player if they join you as host. It is unplayable like this, and really should've been fixed before releasing. The issue is widely discussed on the internet and here in Steam's discussion threads for the game. The issue is with the game's outdated code (written back in the days of dial-up), and not anything to do with my or friends' connections -- I have 200meg, and myself and those same friends get 10-20ms ping when playing other games together. See for reference: https://steamproxy.net/app/976730/discussions/0/2146469724200258510/ https://www.reddit.com/r/halo/comments/e6tlk7/mcc_pc_coop_input_lag_potential_fix/ If you plan to play single player, game is fine (the reskin is underwhelming at best, though). However, if online Co-Op is your aim, either look elsewhere or hold out for the unlikely event this gets fixed. I wish I'd known about this glaring issue before buying -- it makes the game unplayable in Co-Op (which is a shame, as I really do love the game, and was looking forward to replaying it with Steam friends...). The devs trying to make the game pretty rather than playable in Co-Op was a bewildering development choice...