What makes good co-op games?

Lets talk about what makes co-op games work. This first post is just to get the discussion going about what makes good co-op games.

Do you play Co-op games?
What are some good examples of fun co-op games? What makes them fun?
What are some bad examples? And conversely, where do they fail?
What might be some wonky ideas that would make an awesome co-op experience?

I've had the most fun with Co-op games playing Gauntlet, Magicka, Of Guards And Thieves, Risk Of Rain, Planetary Annihilation, Starcraft, Payday 2, TC Splinter Cell Blacklist, TF2 & BF3.

I think one common trend they all have is that the different classes or play styles lend themselves to work with the other classes or playstyles. In Magicka particularly, you have to heal each other and you can even combo spells together for bigger spells. In Gauntlet you could be totally screwed without the other teammates because of the type of support they offer to the team. In Of Guards And Thieves the combined tactics between players is critical for advancing past intermediate enemy teams. In BF3 you could go significantly further with a balanced squad and a support sniper, same goes for Payday and TF2...

So it seems like having those gaps where one player cannot really go the whole distance by himself and is required to work with teammates that are handicapped similarly to the extent that its 1)more fun 2)easier 3)more interesting to work together toward the goals. Risk Of Rain was fun for me to play with friends, but I think the way it scaled made it less important to have team mates around later in the game due to the way the loot system worked. But, the insane effects you got from the same loot system was hilariously fun at the same time, so it balanced out somehow.

Thoughts?

 

Portal 2 was a good example. They had a separate level set for cooperative play. The levels were designed so they could not be completed by a single player. That's good co op play. Co op play on levels that can be completed singly kind of defeats the point.

 

It's not about classes or similar things; It's a much, much simpler factor. What makes a real coop game is that it creates the need for a team.

This sentence pretty much sums up the most important difference between a coop game and a game with coop mode.

Let's compare Borderlands to Left 4 Dead.
In Borderlands your friends can join in or you play alone. Either way you can beat the game and it doesn't make much of a difference. Your friends might as well not even be there. Borderlands is no real coop game since coop is optional.
In Left 4 Dead coop is not an option. Taking on hordes alone is extremely hard and most of the special infected have the ability to defeat you in a single blow unless a friend saves you. You need your team, you want to stick together and you want to help them to the degree that seeing a team fail, because they went back to help a single teammember isn't a rare sight in L4D.

Since separate levels for coop and singleplayer aren't always an option, I recommend you to study Portal 2 and the Left 4 Dead series.

 

Take a look at Trine and Trine 2 as well. They are quite fun games to play with friends, but the fact that you can complete any level alone really puts you off. In fact you are often in different parts of a level, because one player is faster than the other and he can then clear that part of the level alone.

As the others say, a good co-op game is a game where you need to cooperate with other players in order to make progress.

 

Not necessarily a "video game" (it's actually a "hybrid", combining a board game with a mobile app), but the X-Com Board Game is a co-op game. Each player takes on a different role and has their own part to play. So, as you've already noted, it's largely about each player being given strengths and weaknesses, so everyone has value, but they are ultimately incomplete without their friends.

 

This is actually a good point. The coop mechanic is far more advanced in board games then in video games.