The Q400 somewhat fills the gap between small jet aircraft like the Learjet 45 and larger airliners like the A320. The Q400 has a lot of power (5000 horse power on each engines, total of 10150 hp) compared to its mass (max only 30,000kg) which gives it a large operating range and a lot of headroom and makes it a great work-horse so to say. On approach the Q400 can be as fast as a typical airliners which is nice for scheduling in real life and with its large props it can also do quite steep descents and slow down a lot. With it's maximum flap setting of 35° it can also fly very slow and land on shorter runways.
Compared to say an A320 it is still very hands on and but the systems are kept quite simple which is allowed due to its short flights.
The auto-flight system is a bit different compared to the other airliners (but similar to the LJ45) which makes it a nice learning experience. I can for example prepare an ILS on the copilot side while I fly on FMS on my pilot side and then switch the nav-source for the autopilot across and fly the ILS.
Also the handling of the engines is different, in the end it has turbo-prop engines and no turbo-fans. The turboprops are a lot more efficient in terms of fuel consumption which makes it ideal for short hops. And the turbo-props require a bit more monitoring but allow for more customization. I can for example, set 850RPM (used for cruise) but override the maximum torque value to use the climb power. Or I can leave the RPM at 850 for landing (better for noise and vibrations etc.) and arm the 1020 max RPM for a potential go-around.
And I think it's this short range design of the Q400 that makes it so attractive to a lot of users. You can land on A LOT of shorter runway in the sim (I managed to put it down anywhere I wanted to so far, even Meigs can be done...). And it has a lot of power to get from A to B quickly or just to fun things. It's versatile and you, as a pilot, are in the loop, tell the aircraft what it should do next.
"fly heading, now FMS, now VOR, maintain current pitch now, yeah, now power to flight idle get that descent going, RPM 850 and hold that whilst I advance levers to 1020 RPM, now only flap 10 for landing, whew this is quick, keep the power in, nice touch down, now do reverse! BRRRRT aw love that sound, alright now tight turn to the right, yeahaaa, lock the controls, cut engines, ding ding ding - it's ok shhh, DING, yeah yeah I know, quiet now!"
And of course the fact that you can do a real engines start in the Aerofly now. That gives users a lot more to play with, pretend to have an engine failure and try to counter the large torque of the remaining prop at full power. Plus the Q400 requires some pilot action in the cockpit if you want to do it right. It's just a bit different to an A320 or B737 and that is very refreshing.
For me the Q400 can be described as "simply a bit more of everything". More aspect ratio, more horse power, longer fuselage, longer landing gear and landing gear is very far apart -> better cross wind landings, more drag if you want to slow down, more power to climb, more things to do in the cockpit, more things to play with the engines, more prop sound, wings are higher on the fuselage, the tail is higher than normal, it's quick, it can be slow and to a tight turn 
So yeah, what do you guys think, what excites you most about the Q400?
