It's all about the story here. It plays just like the Halo you have come to love, except you don't run around as a God amongst men (a spartan). You're just a troop. No shields. No beating down brutes. No chucking grenades 100 yards. No Battle Rifles /sad face. I just finished beating this solo on legendary yesterday and it was TOUGH. You'll start being scared of brutes and dreading hunters. But once you get the hang of it, you'll start cruising.
The story is really cool, but kind of takes more than one play through to absorb it all (kind of goes for any Halo game though). Also, I didn't beat this game until after beating Reach and I got a bit more out of it (if you don't read the books you'll get more out of the story). I would definitely recommend giving this one a go. It's enjoyable and cool to play as something other than a spartan/elite. If you need tips for legendary, let me know!
AC-130U- "You can run, but you'll only die tired."