Written in December 2014, the game is in contant development and I expect it to be geting only better.
I wanted to start by saying it's unpolished gem, but it's not. It's a highly polished gem, fitted into cheap mass produced jevelry and wrapped in gift bag bough on discount last January. If you want realistic flying experience, don't miss it. If you want to treat yourself seriously as a simmer, you may find out-of-cockpit parts of game not dignified enough.
The good: The sim part (simulating planes and their enviroment) is very good - the game is great stick and rudder experience, the planes have mass and inertia, when flying them on the edge of flight envelope you feel them sliding from course, rather than being pushed to the side along set vector with randomized shaking added. The AI planes use the same physics as player, so they don't take breaks from reality and pretend they are jets when pressed to hard. Par the course, some people find flight models unrealistic or simply not what they expected. There are no clickable cockpits like in CloD or DCS, but after automated engine start you get to control most of plane systems (IMHO the biggest missing part is no manual fuel tank selection). To me it has the best feeling of "being there" of all WW2 planes, but I'm stick and rudder fetishist, not clickable cockpit fetishist. There are no stability problems, unfinished plane systems of weird flight behaviour.
The bad: There are ten flyable plane types in the game. More are in the works, but because of sim part being detailed like I said above, making new planes is slow process. Do not expect to see tens of flyables soon, or variants of the same model (like all Bf-109F variants) made by small modifications of existing plane. There are *no* AI-only planes (one is on the way) because, as they use realistic flight physics, they are not easy to make, either. You won't see tens upon tens of computer-controled planes in misisons, either, they are to CPU-hungry for that. The number of players in MP missions is limited (either to 32 or 48, not sure) , devs still work on optimising support of more players in mission as I write. The single player part, or campaign, is something in between proper career from IL-2:1946 and mission generator - you pick stage of the battle, airfield you take off from, plane, mission type (intercept, escort, ground attack, bombing, close air support) and off you go. Missions are generated randomly with variety of weathers and targets, but they aren't as immersive as real career missions - maybe because you get no background on what your target is and why it's important beyond "go and bomb that bridge". There are difficulty settings in game, but in campaign you can use only two presets, normal (icons and automated engine management) and expert (realistic). Instead of adjusting realism settings before mission, you disable unrealistic aids in flight by key command (say, I bound a key that turns all engine helpers off and hit it at start of each mission, to fly with manual engine management but icons on). The mission editor hasn't been released to public yet and is quite complicated so there isn't much of user-made content and multiplayer servers - but what community made so far was of very good quality.
The ugly: The most hated part, which caused many people to give up the game as arcade: the plane modifications (bombs for fighters, bigger cannons, armoured windscreens etc) are unlockable - you get them by flying the plane in question in single player campaign. Most of these mods are non-standard, experimantal, or one-off modifications, but few are standard-issue systems that you can't accss from the start. Also, the campaign includes game elements like experience and player "level" (the higher it is, the more dangerous becomes opposition and flak fire in campaign. I suppose it is meant to make game easy for new sim players and progress as they succeed and learn). Then, you can start the mission in the air, half way towards the target, and abort it on reaxching "exit" waypoint - takeoff and landing are optional - and on lower player levels thare is little action outside target area. So the first impression is that missions consist of going to action point, doing your job, going back. It's not the case, but you have to bother playing through simpler missions to make things more interesting. These are pointless additions to otherwise purebreed sim, and many people can't get past it - some play multiplayer only and don't want to play campaign at all, some call it pointless grinding, some are so experienced they want difficult missions from the start and give campign up as to easy before they rise their pilot level and get to difficult stuff. Make no mistake, once you sit in the cockpit you get a proper sim experience, and once you get your unlocks and rise level to get interesting missions you just have a good mission generator to play with forever, no limits - but the awards that are supposed to motivate players to play are something out of console game.
There are smaller bad decisions, like locking most of graphics options to four preset settings - you don't get to set manually drawing distance for objects or super sampling, you choose high, low, medium, ultra setting and that's it. You have manual control of resolution and antialiasing, though. It made some sense in development, but is pointless now.
All these are pointless design decisions that nobody i know likes, but the developers stay by them. This stubborness earned them lot of enemity and made many people abandon the game, but I have to say dev team is very cooperative with community in most other respects, adding elements requested by players and listening to suggestions of flight model changes. There was some rush to release the game on deadline, so maybe they will replace it with something better once team catches they breath. Or not.