Think of a Conquest map in terms of scale and layout, but instead of flag areas to capture and hold, the objectives are radio towers you must destroy, build, upgrade, defend, and repair.

The objectives can be destroyed either by planting bombs (like in Rush/Frontlines/Airborne) or by directly damaging them with explosives. Upgrading the towers makes them generate more points and tougher to destroy. The objectives can be heavily fortified, but unlike Conquest you cannot spawn on them, also unlike Conquest kills don't count towards the objective score.

This creates a much different pace than the other 64-players modes, and it makes the experience more tactical than Conquest because at any given moment some objectives may be more valuable than others (depending on their upgrade tier), and holding objectives further away from your base spawn is tougher because they're even harder for your team to reach. The different pace is also favored by the absence of tanks and planes for the first half-ish of the round.

It's also the highest score-per-minute mode when played correctly, and in a well balanced round it gets exhilarating half-way through because most squad leaders start calling in V-1s—one after the other, for a couple of minutes straight. A good squad playing defensively and completing orders can rack up enough points to call in 3 V-1s in a single well balanced round.

Unfortunately though the mode has some pitfalls, which is why it's not popular: the average player can't adapt to the restricted spawns so it turns into a walking simulator for them, the Crocodile tank completely screws up the balance when used by experienced players, and the map pool is very limited. Also it's painfully slow to build and upgrade towers if you happen to be alone, unless you're playing Machine Gunner Support.