I have Reach, its pretty good.. I've only played the campaign aspect so far but from what I've read/heard the forge section and the online part are supposed to be really good (especially the expansion of forge). But thats just what I've read.. I'll find out later after I beat the campaign (I always do the campaign first then do the rest..)
In regards to playing it together.. I hardly ever have a chance to play anything it seems so once DoF is in Phase 3 any available gaming hours = there
"With time you shall learn that I was right.."