Cooperative support for the Half-Life 2 single-player storyline is something that has been requested by a great many people, and as such, it is one of our priorities. Some changes to the maps will be necessary in order for cooperative play to work smoothly, but we will strive to keep things as true to the original experience as we can (another thing that has been heavily requested). Partly in the interests of this -- and also due to performance issues, balancing issues, and the fact that the maps were simply not designed with large player counts in mind -- the maximum player count for HL2SP maps will likely be fairly low. Higher player counts will be supported for cooperative maps.

One of the features we mentioned last year is our mapper-defined class system. This (optional) functionality will allow mapmakers to set up anything from simple player model or spawnpoint selectors to full TFC-like class systems (there might be a Hacker class who could break into enemy computer systems, for example) or whole game modes (such as an escort-the-VIP map, or maybe a map where the players are split into two groups... one group defending a position, and the other attempting to rescue them before it's too late).