Reach was AWESOME... I am sure that some people will complain about one thing or another because it is different in some ways from the original. For example the scale is much larger (including a space battle and a gun large enough to kill a phantom in one hit EASILY), the variety of vehicles is amazing, there are a huge number of armor specializations, etc. I, however, felt that all of these changes were positive as the audience learned with each new game allowing for a greater level of complexity without slowing down the pace or hurting the playability.

Other highlights include:
Dark and gritty story with great dialog (I love dark type endings).
Killer chapter names which refer to dialog from previos games (for example: "I need a weapon" and "protocol dictates action!"... It may seem like a small detail but it brings back great memories from previous games and show Bungie pays attention to it's roots.

Only downside I can think of would be the space battle: it's quite fun but very unrealistic: a real space battle would occure at speeds to great for a human operator to control and distances to far way to actually SEE your targets. Morever a host of hard to cromprehend issues would come into play such as avoiding tiny space debris, turning slow enough to NOT kill you and avoiding trajectories which have you escaping or falling into the planets gravity well.