its a gritty and downright refreshing game to play, and it was incredibly innovative and influential. its one of the best pc games of all time because it earned its place on that list, not because people blow loads reminiscing about how fun it is/was. halo didnt innovate shit, it just brought fps to mainstream awareness by transposing the basic pc formula to consoles...and on pc, it kind of just sat there, making money.
Actually Halo 1 did innovate some things. First, it was one of the first games to feature regenerative health. Second, it imposed a 2 gun limit and 8 grenade limit. Other games would let you carry as much as you wanted.