I think you've been slightly misinformed. The protagonist is not "an average soldier." Noble 6 is a Spartan similar to the Master Chief with comparable abilities. In fact, the new armor abilities make the character more capable than the Chief from a gameplay perspective.
I found the campaign to be one of the best in the series. It's definitely a more somber, darker tone than previous titles. Battles as a whole are larger, and missions tend to be more varied, often employing two or three different set pieces per level.
Since you haven't played ODST, you haven't tried Firefight yet. It's an awesome co-op mode where you try to survive against increasingly difficult waves of enemies. You can play it solo or with up to three friends. Unlike ODST, Firefight mode in Reach is fully customizable, allowing you complete control over weapon selection, enemy types, basic player attributes, and more. It's definitely worth a try.
Reach doesn't radically change the Halo formula, but it's taken everything that's worked from previous titles and integrated them seamlessly with a few new features to boot. If you're still on the fence, I'd recommend finding someone who has it and try it out.