I love Reach! I got it Wednesday and am on the last mission on the Campaign. I haven't really gotten into the campaign though, maybe because I'm playing on Legendary and it frustrates me
. Oh yea, if you play on Legendary it's a lot harder than the Halo 2/3 campaign was, but I like a challenge
The multiplayer is extremely fun too, unless you have a bunch of tryhards when you go into Team Arena that just sit and camp the whole game. Team arena is liked ranked and is really cool.
You can customize your Spartan way more than Halo 3, you buy armor with credits you earn in each game/campaign mission.
There's so much to say you just have to play it to realize what a great game it is.