Might as well add my own opinion of this, so here is Raptor's inconclusively conclusive conclusion on Cliffs of Duty:
First of all, performance. I'm running a slightly outdated system (Dual Core 3.0GHz CPU, 4GB RAM and Radeon HD 4870) with the latest preview Catalyst drivers and the Ubisoft intro logo renamed, which is supposed to help, and performance on (nearly) the highest settings is, while not as good as in IL-2, far better than I expected. So far I tested a battle over London with 36 aircraft (12 bombers and 24 fighters) and a battle over sea with 132 aircraft (36 bombers and 96 fighters), and frame rates were pretty good for most of both flights. The major drops occurred when looking directly at London, at which point the frame rate drops but not enough to render it unplayable (This is better than in IL-2, where looking at a major city would make the game extremely slow), as well as when combat was initially joined in both instances, where there were major lag spikes in both cases (Especially the latter one). Most smaller dogfights seem to run pretty well overall, especially when not over major cities.
Right, AI. I found that it seems to do nothing when given a free hunt order, but would engage when given an attack bombers or attack fighters order. As for performance, it displays traditional IL-2 AI h4x by nearly always being faster than you, and I don't think I've seen it stall either. Keeping a tight formation also seems to be still beyond its grasp, as I've seen multiple collisions in my tests, though it could well be that I've spawned them too close. On the other hand, I've been killed by an AI aircraft when pulling a sharp turn, which the AI in IL-2 was utterly unable to do. So, I really don't know what to make of it; more testing is in order.
I'm not going to comment on the FMs and DMs, as I don't really know enough to judge them. I know they apparently have problems, and that they're going to fix them, which is good. All I can really say is that I've been able to keep flying with damage that would've made your aircraft completely unflyable in IL-2, which seems right, but I can't be sure about that.
I haven't really bothered with the campaigns yet, but they seem pretty bad, especially the British one. IL-2's stock campaigns were never very good anyway. I wish they had the dynamic campaigns they promised, and hopefully they'll add that in a patch, expansion or something.
As for the rest. The FMB is significantly more useful than IL-2's, with loads of more features, which should help with making interesting missions. I really like the clickable cockpits and more complicated startup procedure, as well as the (apparently) more realistic engine management compared to IL-2, which sort of makes up for the significantly lesser amount of flyables. The new radio chatter is nice, since the AI actually tells you what grid it sees the enemy in, and I've also seen bombers call out what targets they're seeing. Having to open or eject the canopy when bailing out is a nice touch. Also, ammunition belt and bomb fuze customization.
On the other hand, it seems that radio commands are broken, and that they're working on fixing it. This is pretty big oversight, or it would be if the AI ever listened to what you were saying in IL-2. The interface is an absolute atrocity, and it makes IL-2's look like the most modern in the world. Anti-aliasing seems to not work very well even on the highest setting, especially on distant objects. Oh, and the Heartbreaker.
Overall, I don't find nearly as horrible as I thought it would be. It still needs a load of work, but at least they're still patching it, unlike a lot of other games these days. We shall have to wait and see how it turns out after a few patches and expansions.
And I don't find the (menu) music that bad, not nearly as much as IL-2's...