One of the games that my brother and I have been playing a lot of over the last few months is Lost Planet 2, the third person shooter made by Capcom. The game's strong emphasis on co-op gameplay makes it a great game for our purposes. However, the game definitely has its mix of great stages and poorly designed stages. After a while, I think I have noticed a few patterns, which could be taken as lessons to be learned for future games.
Ironically enough, mission 1-1 is one of the hardest stages in the entire game, particularly at higher difficulty levels. This is entirely due to the final segment of the stage, where the players have to seize and maintain control over a mine. There are two main causes for this difficulty. The first is because of the open layout of the mine; it consists of a large open central area surrounded by multi-level structures with lots of open doors and windows. Essentially, every enemy in the mine area can easily get opportunities to shoot at the players, meaning that the players have to deal with all of the enemies at once, making it easy to get swarmed or surrounded. Second, the game asks the players to maintain control over four control posts at once for a certain amount of time. Because of the spacing of the control points and constant reinforcement of enemies from multiple entry points, this is very difficult to do with even two people. It feels like this part of the mission more or less requires four players in order to be easily feasible.
This second point is seen again in mission 5-1, where the players are asked to once again maintain control over certain control posts for a certain amount of time; this time it is two control posts located in different rooms separated by several corridors. In our case, my brother and I were each able to guard a room, but it was a very difficult fight for us, since powerful enemies constantly stream in from three entrances into each room. Based on these missions, it feels like missions that require maintaining control over multiple places at once vary in difficulty a lot more significantly based on the number of players than missions that require simply advancing forward. This is probably because these missions force players to split up, which is more punishing for two players than for four. I have no idea if it is even possible for a solo player to tackle these (disregarding AI helpers).
Perhaps a more positive and interesting way the game takes advantage of its co-op focus is in its stages with multiple routes. Most stages in the game are very good at having at least two routes to get from one room to the next. For example, 4-1's first area consists of a multistory building. Many floors in this building have two or even three stairways leading to the next floor. This opens up a lot of room for strategy. The players can all go down the same path and try to combine their firepower, or they can choose to split up, take different routes, and flank the enemy. This multi-route design even lets players split up to clear out enemies and independently secure objectives if they so wish.
On the flip side of the coin is the final section of mission 4-1: a narrow choke-point leading into a large area where there are multiple heavily armed mechs ready to shoot anyone passing through the choke-point. To make matters worse, the only weapons capable of talking out the enemy mechs are on the other side of the choke-point. This kind of design comes up in about three or four places in Lost Planet 2, and it really is inexcusable. In all of these occasions, the only choice is to make a beeline for the usable mechs or good weapons and pray you can find some cover before the enemy fire tears you to shreds. This kind of area layout gives an overwhelming advantage to the enemies, and can quickly become very frustrating to the players.
On a final note, I really liked the co-op cannon segments of the game. In these, all of the players need to to work together to man powerful weapons against giant enemies. While one player is aiming the cannon itself, other players are manning anti-aircraft guns to hold off threats, fighting off enemies who have boarded the player's vehicle, or working to power-up the main gunner's next big shot. These battle can be frantic, complex, exciting, and very epic. Unfortunately, I gather that they aren't very fun when one player is playing solo. That is a real shame. Unless the game designers can write AI that can actually behave the way a player wants them to in such a complex situation, this is going to remain a trade-off when choosing between making a primarily co-op vs single-player experience.
I think there is a lot about Lost Planet 2 that shows that a game built around four player co-op does have significantly different level design considerations than a game built just for single-player. As a big fan of co-op games, I do kind of wish that there were more games like Lost Planet 2 out there.