I picked this up 2nd hand off Amazon for a tenner.
Money well spent
This game came out a year or 2 ago, something went very wrong in the original release and the game ended up on American shelves only 3/4 finished, subsequently the game got slated for being released in an incomplete state.
Anyway - this was re-released with the first long awaited patch and what a little gem it is. The game is open-architectre, anyone is free to create terrain, planes, explosion effects (one guy is making a tactical nuke which is very near completion)
The sim is based on the early US jets of the 60's, all engine, no frills. No head up display, merely a gunsight, you lock a sidewinder on by listening to the audible tone as you get the bogey in your gunsight - the dogfighting is out of this world, and beats LOMAC by a mile in my opinion, guns guns guns and unreliable missiles - incredible explosion effects, debris, the feeling of speed as a Mig 17 flashes across you with guns blazing has to be seen to be believed
The best bit about this game is the community, loads of talented 3D modellers producing free add-on aircraft which are every bit as good as the stock planes that come with the game, Harriers, Migs, A-7 Corsairs, the amount of quality stuff available for free download is staggering.
Aside from the default desert map, I have Vietnam, Europe, America Northwest and North Cape, all made by 3rd party modellers and artists, and its getting better and better.
http://www.max-gs.com/adave/
Multiplayer i haven't tried yet, but I've been assured it is very good, but like all other aspects of this game its a rough diamond that needs a little polish.
And you don't have to strip your PC down to a no-frills hot-rod to run it either