I can so relate to the love of flying in old videogames! On our old Windows 95, we had Fury 3, and I would spend hour after hour playing that--not just to win the game, but just to fly, because it was so much fun!
For those who haven't played it, you basically have this little fighter that you fly around to different mission objectives on a planet. Once you've completed all objectives (which were usually something like "Fly to Checkpoint A. Then fly to City B and kill target. Then fly to City C and destroy it. Then fly through Tunnel D, etc.") you flew to the "Jump Zone", which teleported you to another place on the planet. After three missions, you went to the next planet. As you flew around, you picked up more and more enemy fighters around you, which you destroyed by shooting them down with increasingly powerful weaponry you picked up from blowing up OTHER stuff.
So pretty basic, but the fun thing was that there were no limitations whatsoever on where you could go or what you could do--scenery was extremely limited, especially outside of the areas you were "supposed" to go to, but it was all explodable, and you could even completely skip mission objectives and go straight to the Jump Zone if you wanted to. And flight was AMAZINGLY fun! I used to do crazy loops and skim as close to the ground as possible--I think I even managed to get a couple of enemy ships to crash like that once. And you could even fly beyond the cloud cover into the upper atmosphere (or whatever it was; graphics were terrible back then), so there was all sorts of maneuvering moves you could make, and even a limited turbo speed to cover lots of ground fast.
All in all, it was incredibly fun because it was so open. The planets were technically limited, but it wasn't obvious, because after a while you looped around to where you'd started from. The controls were easy to pick up and simple to use, and could do pretty much anything you put your mind to. And the freedom was great--you could do each mission objective, then go at turbo-speed to the next target and so on, but it was a lot more fun to meander around and kill everything in sight instead (besides, you got all sorts of lovely bonuses and extra points from that!). We need more games like this. It had scarcely any plot beyond "aliens taking over the galaxy" and terrible graphics, but it was fun, and that's all that mattered! *sigh* Nostalgia. I'll have to go play that game again now...