We've got a 2013 5 with the 6-speed. Fun to drive, it acts like a much smaller car. It's easy to find yourself in the wrong gear, though, as it doesn't really have a ton of torque at the low end. Or, really, at the high end, if we're being honest. It's not a fast car, but it is really nimble compared to anything else that has 6 seat belts and 4 wheels.
If you're moving adult-sized humans, it's a 4-seater. Around town, we will take short trips with all five of us, but often my wife will sit in the back because she's Korean enough to fit back there. I don't have a snowball's chance in hell's kitchen of fitting, and the teenage girls can fit, but it's not a real elegant process. Longer trips are pretty tough.
Devoid of people, you can put the seats down and get a good amount of room, but like Tim says, bikes don't stand up. Despite the sliding doors, it's really more of a 3 wagon than a minivan. We've moved some big, bulky things with it, though, and it's not been a problem. The hatch opens wide and it's low to the ground for easier loading. The dogs like the space in the back with the third row down. Speaking of the third row, it's a split configuration so you can put on seat down for some space if you're moving 5 folks. With the seats up, however, there is almost no room. A gallon of milk and a couple bags of groceries is all you get. There are some good D-rings back there for tie-down purposes, though, once you put the seats down.
I find the seats to be comfortable and you seem to get a somewhat upright position compared to a 3. The armrests are kind of chinzy, but they swing up out of the way when you don't want them and they provide pretty ergonomic positioning when you flip them back down. I don't know, I just feel like I'm going to break the things. You couldn't get the third pedal and bluetooth or leather seating, so if you want those things you'll need to figure that out on your own. I added a double-din digital media head unit to ours. If you do that, don't put your microphone in the factory location under the dash over the gauge cluster. That might work for whatever microphone Mazda uses, but your's will pick up the driver's voice faintly while providing the other end of the call with a front-row seat to the sound of your turn signal. Maybe it's just my kids, but the cloth seats have seemed to have attracted every stain within 30 miles.