In fan game standarts, this game is good.
The game itself is sort of boring, if you look at it as a fan made spin-off. There's basically no storyline, and the only fun in it is shooting off the enemies or throwing a grenade at a group of the Covenant. Even riding the Warthog is boring, and you can't pull off stunts like you could in the original game. This game could be much more, and instead of this it's quite disappointing.
The game interface is designed poorly. Some of the graphics were ripped off the PC version of "Halo: Combat Evolved" and look very inappropriate in a completely 2D-based game. On the other hand, the game graphics may please the eye of a player who's familiar with sprite-based 2D games.
The sound effects are implemented well, and the music sounds good. The comments uttered from the Covenant enemies, however, are of a poor quality and somewhat ruin the feeling of a game.
I still haven't checked out the multi-player feature of the game, but it looks promising, though people are complaining about latency problems (lag).