I recently discovered this War Thunder game and at first I didn't think it was too good and quit after only about 20 minutes played. However, I went back to it and was shocked to see how much fun it is. I don't know that I'd classify it as a direct competitor to Aces High, but it certainly has several aspects where it outshines AH.
1. Terrain Graphics - This completely blows away Aces High, looks so much better and makes the environment much more immersive. The was clouds and flak are done is downright amazing, it really puts Aces High to shame.
2. Instant Action - Yes it's arcadish but it gets you into the fight *fast* less time wasted than the typical MA session where you might putter around for 20 minutes looking for a fight often to have it end before you even arrive.
3. Free2Play - I've spent nothing on War Thunder and had several hours of fun with it in the past couple days. Aces High is *still* charging $15 subscription just for a month's access regardless of how much you actually play.
4. Learning Curve - Starting new players in Arcade mode with simplified controls and fast basic tutorials makes the barrier to entry so much smaller. I've tried dragging several friends into Aces High, and unless they had a very dedicated interest in learning all the complexities involved they tended to quit. War Thunder starts you off in easy mode and lets your work up to the more realistic settings (I haven't gotten to those yet for comparison).
5. Playerbase/Average skill level - This game has a huge playerbase so finding a match is quick and the majority of players seem to be downright terribad at the game. I routinely dominate stats for my team sometimes racking up a dozen or more air to air kills in a single mission. A little bit of ACM knowledge really does help dramatically against the hordes of unskilled n00bs even in the arcade mode.
The Downsides:
1. Leveling system forces you into prewar trash tier planes to start with, and it takes a bit to even unlock historic or high realism modes.
2. No long term persistent world Arena with strategic objectives. This is probably most detrimental to the bomber players.
3. GVs not implemented for player control yet.
4. Flight model at least in arcade mode is a lot more simplistic than Aces High
5. View controls are a lot more limited/primitive
6. Damage modeling is also a lot more simplistic than AH and certain planes seem able to absorb a lot more damage than realistic
7. Simplified gunnery with lead indicator (not sure if this goes away in higher realism modes)
In short, I recommend it. It's surprisingly fun for no cost.