I've been playing through the ps2 Ace Combat trilogy recently. Great fun. Soundtracks and sound effects are all wonderfully made too.
May I interest you in some sound effects?
I'm still hoping people will decompile and port these 3 games on pc, I'd love to use those models (and level models) on SFM or Blender. As well as playing it on PC and not on an emulator.
It's an amazing series. I've never finished AC4, but after the recent PCSX2 updates it became pretty playable without any issues and I finished it for the first time. The jump between engines from 4 to 5 is really noticeable, the lightning is amazing. 5 Has a huge issue with pacing, I really don't how some missions basically have you twiddle your fingers while you wait for the next set of targets (namely, the mission where you sink the first enemy nuclear submarine and the other mission where you escort the president's plane). Zero is amazing but fully completing that game is a bit of a bitch, since some aces are really finnicky with their spawning conditions.
If you haven't already, also play the original trilogy for the playstation, Ace Combat 3 is amazing if you can look past some of it's flaws (like having to use a fan-patch to translate the game from Japanese to English and still not being really correct).
Also, apparently all of these games were rushed beyond belief, and according to rumours, 5 was supposed to have at least 3 more planes, one of them had the burst missile special weapon which was later used in Ace Combat Zero.