Halo definately revolutionized gameplay for first person shooters...just look of Halo 2s popularity
The graphics were good and the weapons and characters seemed realistic. Blood spatter effects are cool and the drivable vehicles are awesome. The maps are interesting and immerses you in feeling like your on another planet, especially the Flood levels.
Frame rate is steady, but lets talk about mutiplayer. No LIVE, but LAN is just as fun, especially when you can get a good amount of players...I know because even though I got Halo 2 first, I used to go over and play Halo CE before 2 even came out.
Levels are awesome and controlling a tank leaves you feeling vulnerable but at the same time powerful enough to dominate the map. Blood Gulch is probably the best and most popular mulitplayer level, for it was converted to Halo 2 and rename to Coagulation.
Halo is a good game, but if you have to choose between this and Halo 2, (If you have LIVE) choose Halo 2.