Major appears as a statue in the first map, "Arena Gate". Major was the opponent in the Q3 demo version of that map.
Doing It for the Art: For a multiplayer-oriented game, there's a lot of effort put int it to make the game as enjoyable as possible.
The bots are only there if you don't have enough humans to play the game properly, and they're made for fighting rather than talking, but they will still chat at great length about anything, particularly if prompted by the player. They'll sometimes seem to make sense, rarely repeat themselves and never say anything less than true to their individual characterization. And there's thirty-two of them.
Live's Training map has Crash taking you into a course, for a latter fight against her. There's even voice acting and all.
The game recycles several sounds from Quake II, namely the Quad Damage activation sound, the Invulnerability wearing off sound for every other temporal item, the Invulnerability activation sound for the Battle Suit, the Grenade Launcher's sounds and the BFG shoot sound (that one which it does after charging) for the BFG shot.