I love the aircraft, and I love how absolutely enormous the game's environment is. I've run around for a couple of hours and have probably seen about 5%-10% of the landmass, and that includes flying over it in planes and helicopters!
There's also a really cool contrast between creating tons of chaos in the form of towering explosions and then jumping off a cliff and peacefully para-sailing just wherever your whims take you. Missions pop up all over the place and can be done in any order. The game actually encourages you to run around and do whatever by doling out rewards and unlocking story missions based on how many side things you do (mostly destroying government infrastructure). It's great to jump into and mess around with such a huge and good looking open world.