Yea I have easily spent multiple thousands of hours playing the Halo series, so I do consider myself very experienced. Definitely played 1 and 2 the most by far though.
Only had time to play 2 games last night, as I am in final exams week, but it was very cool. The game itself looks sharper visually than all the others (even on my shitty mini tv), but that is to be expected. As far as gameplay goes, it is a very different game.
At the start of the game and at each spawn, you get to choose 1 of 4 specialty moves to spawn with. Here they are
1. Jetpack - you can fly for limited amounts of time with a jetpack. The amount of fuel you have is noted above the radar, and taking your hand off LB restores your fuel.
2. Stealth - you are invisible when crouched or standing still.
3. Action - you can sprint for limited amounts of time, like jetpack.
4. Defense - this is the one I know the least about. Your spartan pounds his fist into the ground, creating a field of energy (which I believe hurts enemies in your immediate vicinity), while you keep holding the button down, you are invincible to MOST enemy attacks (I believe bullets and explosions at least).
But yea, that should give a brief idea of the new things available in Reach. Although there are only those 4 special moves, they greatly alter gameplay. It really shakes things up when an invisible guy pops out of nowhere, and equally catches you off guard when 2 or 3 guys randomly drop out of the sky above you on jetpacks.
I'll be really interested to see what other lifelong fans think about these new changes, as they offset the balance of power that Halo has worked so hard to create from the beginning. I remember the days of joking with my less experienced friends and telling them that my masterchief was faster than theirs, and saying elites could jump higher, and stupid stuff like that. But now there actually will be instances when I'm trying to run away with a flag or something and other players are faster/can jump higher, etc. This will really change up strategy.