So that's the basics of co-op, but what about the execution? Unfortunately it's a mixed bag. It's a very difficult mode, especially your first time through, which is a result of a few different factors. First, the initial wave of enemies can easily overwhelm your team, with one or two members dying before they even realize whence that hails of bullets came, mainly due to there being no radar or enemy tagging feature. The lack of a radar is a carryover from the game itself, where you don't get any such device but instead are forced to rely upon a (very unreliable) echo location system; but even that isn't available to you in co-op. So, you're forced to eyeball everything and rely upon team communication, which isn't a bad thing assuming your team actually communicates. If not, then the loss of one or two teammates right from the start can mean a quick loss due to the "pay to respawn" system.
Second, the mode as a whole feels artificially difficult, which can be quite off-putting. Part of this difficulty is due to the damage dealt by the starting guns of each class. This is no doubt an intentional design, as it helps to focus the team more on working together to take down foes rather than every man being a solo killing machine, however, it's also tiring. The third or fourth time you die to an enemy and you know you got off a good five or six shots into them, but they're still moving, you'll start to beg for more weapons. While there are other, slightly more powerful guns that are available to each class, these can only be unlocked by completing different tiers of challenges.
These challenges are either class specific, like "kill x number of enemies using the Tactician's turrets," or more broad, such as "kill X number of enemies with a headshot," and can only be completed for the current class you're playing in a match. What's more, you have to complete at least two tiers of these challenges before you unlock your first gun, and that's not something you're likely to complete within just a couple matches. It's a good idea as a way to incentivize people to use their abilities and play the co-op mode, but it comes off feeling like a chore. The net result of all this is that the mode is not welcoming and quite frustrating unless you become fully vested in it.
It's hard to get too invested in the mode due to the final factor: the player requirement. Intercept feels like it was designed to be played with four players at all times. It's the second part to the mode's artificial difficulty. With a solid team that is communicating, knows their class, and works well on retaking and defending the strategic points, then matches can be tough but manageable. Three players that are well coordinated and select the right classes might be able to manage a Quick or even Regular match; two players is next to impossible and solo play is a waste of time. Understandably, the player base is rather small at this point, but even when you do manage to get a full squad of randoms together, chances are good that it won't be a fun co-op experience. If even one or two players are constantly going off on their own and not working with the rest of the group, you'll probably play a game or two before moving on to something else altogether.
All of that being said, there's still some fun to be had in Intercept. Even if it is artificial, it's a good challenge for a solid co-op crew, and there are "just barely made it" and "come from behind" victories to be had/enjoyed. So, if you've got a co-op crew that all has the game, $10, and an interest to play, then you're set. For everyone else, the mode may be prove to be entertaining for a match or two before ultimately turning into an exercise of frustration.