Bicycling industry titan Shimano is renowned for quality and reliability - they are the dominant bicycle components used by cyclists of all levels, right up to professional riders. Like Brose, they came to the party a little late but they keep carving off a healthy chunk of the eBike market. Their entry level Steps E6000 is lighter and more affordable than Brose or Bosch, and the performance is no slouch compared to the Bosch Active line. Like Bosch, they use a proprietary battery along with their motors. Shimano is getting traction with mountain bikers with the E8000 motor system that is lighter than both Bosch or Brose yet has plenty of gusto to climb hills. Batteries for City systems are externally mounted on the back rack or frame mounted on the downtube, and on the small side at 400 watt hours. Integrated batteries are coming for some eMTB in mid 2018.
The Steps systems have impressive technical capabilities such as integrating with Shimano's cutting edge Di2 electronic shifting, with some configurations capable of auto-shifting, a feature popular with entry level eBikers not accustom to downshifting when coming to a stop. They are the lightest weight and least bulky of the big three, which can really make a huge difference in handling and performance.
Shimano has impeccable racing credentials, so they have really stepped up their game to distinguish themselves with the MTB focused group. A full 2.5 lbs lighter than Bosch's Performance CX, it also has the narrowest "Q factor" and allows for shorter chainstays. Just because it is lighter does not mean it is not powerful - it has 70 Nm of torque - in real world testing it is neck in neck with Brose S, and just shy of industry standard Bosch Performance CX.
Q factor is the distance between the pedals - further out and the bike handles funny and pedals can dig in on hard corners. Shorter chainstays gets the wheel tighter in under the rider for more traction on steep climbs - something bigger drive housings like Bosch have a problem with.
Broken displays and controls are becoming an annoying and expensive part of eMTB - when you are really getting the most out of trail riding, the bike will go down eventually. If your display and controls are on top of the bars, they are vulnerable to being smashed. Pedaling your 50 lbs bike back without power is no fun, nor is shelling out hundreds of bucks for replacement parts. So the eMTB setup keeps them safely under the handlebar where they are less likely to get broken.
The mode selector on the eMTB system is very intuitive for regular mountain bike riders - it is on the left side under the handlebar, where a front derailleur shifter would be on a non-electric bike. Since 1x drivetrains has enough gear range to do away with front gears, now there is room right there. It feels like your shifting gears when optimizing the mode assistance for the terrain you are on.
Integration with top of the line, butter smooth Di2 electronic shifting is another outstanding feature only available on Steps systems at the moment.