While I generally like Halo, I would have to say that yes, the game is in fact derivative. Just a quick listing off the top of my head:
1) The main character is a power armor wearing space marine. While the powered armor and branch of service vary immensely, this idea has been common for ages. WH40K, Doom, Star Craft, Crysis and dozens of others have explored this concept. Generally this is done so that the obstacles the player is required to overcome seem reasonable because:
2) The player character is the only one who can save the city/country/planet/species. This is such a common narrative concept that you'll find it in games ranging from Galaga to Rainbow Six Vegas 2.
3) Aliens hate humanity. Maybe it's because of the fact we have five fingers and our skeletons on the inside. Maybe it's because we littered on the wrong planet. For whatever reason, in most video games Aliens seek to exterminate humanity for little discernable reason. In Halo, religious fanatacism drives the extermination attempt.
4) The group the player belongs to is on the ropes and is about to lose the conflict. Doom, Command and Conquer, Killzone, Quake, Duke Nukem, Warcraft, Dragon Age: Origins - countless games leverage this concept.
5) The only thing worse than one alien is another alien that seeks to consume all life. The Flood represent the true threat in the Halo universe, but the basic concept for the creatures can be found in things like Alien, Starship Troopers, Starcraft, WH40K and so forth.
6) Humanity is always outclassed and outgunned. No matter how advanced human equipment, the aliens always have something fancier. Starcraft, WH40K, Duke Nukem, every space shooter ever made and still others leverage this concept regularly.
Not only have these things been done many, many times before, they've often been assembeld in roughly the same way (Quake for example).
Also, as a counter-point to the "Master Chief is a quality character", I would assert that you must have been playing a completely different game than I did. In the game, he is nothing more than a suit of armor with a gun who stoically guns down the enemies of man for no reason save that he's the only human lucky enough to have power armor. While I'm sure there might be better characterization in other media, none of this was present in the games themselves.