Never tried WW2OL, but I've played IL-2 multiplayer sessions side-by-side with AH for quite a long time, and enjoyed both games thoroughly without any bias. Personally I have the utmost respect for both HTC's AH and 1C's IL-2 as being a great WW2 aerial combat simulation game.
Frankly IL-2 series is not really as bad as most people in this thread say it is. Whatever you can do in AH, you can do most of it in quite the same manner in IL-2, and vice versa. The only really visible/obvious difference in FM is how they handle the torque - in AH the torque effects of individual planes are very prevalent and characteristic, and often powerful enough to quickly flip the plane over by itself even in perfectly normal, level flight conditions, whereas in IL-2 the torque effects are depicted as being much weaker, and very gradual in its effect to a plane in flight. This is what makes the plane feel "generic" in IL-2, which, it is not. The differences between planes are much more subtle than in AH, but it is there.
Other differences are much more subtle, and yet effects the game at a very fundamental level - which is another big reason why most AH gamers cannot really adapt to IL-2.
For instance, the ever-famous visual system - the restriction of views in IL-2 was a major let-down even when the very first of its series appeared in the market. Despite having a very successful view system to benchmark in the form of AH, IL-2 chose a primitive restriction where pilot head positioning inside the cockpit was entirely denied. (It was later revealed that this was due to how the cockpit was visually modelled - ie. "facade" type of modelling, rather than the true-3D modelling AH uses, in which the developers had to restrict head movement, or otherwise the optical illusion of having a "3D cockpit" would fall apart at different head angles)
This directly interprets into a serious limitation in visual information during combat, which results in the combat dynamic of IL-2 being much more conservative and defense oriented (..and to a degree, ironically, 'more realistic' in some cases) , rather than the far-more aggressive combat dynamics allowed in AH: even if it is possible to use the same tactics and pull off the same maneuvers as in AH FM-wise, the limitation in visual info makes it much more difficult to do so. Therefore most usually combat maneuvering in IL-2 tends to revolve around the simple principle of "avoiding being bounced", and "never lettings someone behind your six" - in contrast, many capable veterans in AH rather enjoy those kinds of situations where they'd keep constant track of enemy movement behind them, and use a variety of tactics to overshoot the enemy or turn the tables. In IL-2 it's much much harder to do so, so people would rather stick to the basic combat principles, rather than take the risk.
Another such example would be the gunnery. The gunnery/DM in IL-2 is perhaps the single most defined system which actually outshines AH, and differences in armament manifest in very different ways than just the raw power of the gun. There are a lot more parts to be damaged in a very different manner than in AH. For instance, I've actually experienced the following event: I've shot at a Spitfire wing with a 109 MK108 30mm cannon at a close range, from a top angle. The shell landed on the broadside of the wing, and then actually went through the wing, and detonated at the other side as it exited from the structure! The Spitfire obivously got a great big hole and a very widely tattered wing surface, but the structure held intact. In AH that would have constituted an instant wing-snap.
This kind of sophistication really brings out the difference in armament - as in machinegun-class weapons needing a very concentrated shot to really damage an enemy plane, and in most cases the final kill-factor comes from starting a fire or killing the internal engine system causing a great big black smoke, rather than a catastrophical structural failure. While it is certainly possible to snap a wing or blow out the entire rear fuselage with 50cal-armed planes in IL-2, it is much more inlikely to happen than in AH. On the other hand, the cannons do blow out whole pieces from the enemy planes, and most of its kill-factor comes from causing structural failures.
Another factor which is subtle, but deeply effects the combat, is the lack of ammo counters and icon information. Although it is possible to see exact enemy distances, most multi-player rooms restrict the icon info to the basic faction/plane-type standard, which distance information is usually omitted. Since you have no way of knowing how much ammo you have left in most planes, people tend to veer away from trying long-distance shots in IL-2. Most shooting begins within approximately inside 200m in IL-2, which is about twice as closer than in AH where people usually tend to consider the "400" range marker as the optimal shooting distance. Ofcourse, some very talented pilots do try a long-distance snipe with incredible results, and it is certainly possible as it is possible in AH, however the odds of such things happening in IL-2 are indeed, much more slim than in AH. Therefore the average gunnery difficulty tends to be a bit higher in IL-2 than AH, with the side-effect of that being that you have much more chance of survival even if an enemy planes latches behind you at a very close distance. Therefore, while close-quarters knife-fighting is far less common than in AH, when it does happen it does offer a very interesting fight.
...
Now, all of what I've presented above, results in the fighting styles and tendencies of IL-2 being very, very different from AH. It's basically not so much the FM which brings out the difference between the two games, but rather the difference in the entire environment which encourages the pilot to fly differently. Most AH gamers who try IL-2 for maybe a month or two, never get past that adaptation phase, and in the end just gives up on the game for being garbage - which, it is not. I know that for a fact, because I was the same. I also had a very difficult time adapting to the differences, and tended to think AH was better in every aspect. I never gave the IL-2 fair chance to grow on me - until some of my friends who've never tried AH, started flying in IL-2. So I really didn't have any choice but to fly with them, and after a long time, a lot of the things which I couldn't understand in IL-2, finally started to make sense.
All in all, IL-2 definately is a worthy competition to AH.
I'm sure many of the AH enthusiasts would tell a new player to try AH for some time, and not be judgemental about the game with only a month of two of experience. Try to keep an open mind, accept the differences, learn from the more experienced players, and gulp down the pride and be humble about everything until he begins to understand what AH can really offer.
I can certainly say the same to all the IL-2 bashers on the board. Usually, it is because many of the AH gamers that try IL-2 are already experienced and capable players, that they tend to refuse to accept that they might be just another newbie who needs time to adjust in a new game. Many tend to think being experienced in AH will automatically enable them to show the same level of success when they move to IL-2. Since both games feature the same planes, and same era of aerial combat, once the player gets past that adaptation phase naturally they soar right past the learning curve and become terrific players in IL-2 too. However, there's no way to speed up the adaptation phase, which usually is a very frustrating experince.
I'm not sayin IL-2 is perfect. I still view more highly of AH. Some aspects of IL-2 are noteworthy, and I'd certainly like to see some of those stuff implemented in AH as well, but other aspects of IL-2 are indeed lacking when compared to AH. The user interface is terrible, view/control systems suck, to much attention to techincal detail actually deterr situational reality in many cases, and etc etc.. But it's certainly not garbage. It is a worthy successor to the line of WW2 combat-simulation packaged games that include AoP, AoE, and EAW.
IL-2 at leat deserves that much.
