Having the starting weapon as shotgun wont teach anyone anything. The shotgun's flaws in halo 2 drag down a player very easily. And having no shields on? How would that teach someone to kill fast, they wont have to try, just pull the trigger in the general direction and let the shotguns spray talk. It also is flawed in that it wont teach people to work as a team. It would be a group or two, with your rampant lone wolf running around dropping on people and shottying them.
Now, a good gametype to teach some skill is a gametype with a battle rifle start, nades on, no radar.
The lack of radar almost forces you to work as a team because the battle rifle start makes you instantly vulnerable if you are alone and the other team is being just that....a team. Even splitting in two's can allow you to wreak havoc with BRs. BRs are basically the new pistol. Using nades will teach you to kill quickly, no more newb combo bullshit. Nail a splash damage from a frag, headshot once with the BR is an instant kill. This will also teach you how to lay plasma nade "traps."
That is, retreating from a fire fight with an oponnent whil dropping plasmas in your wake. If the opponent is stupid enough(which most are) they will try to dodge the plasmas and lose their shields. At the time, you swing around pop a headshot with the BR and hear GAME OVER as your team takes the match.
Wow I just went off on a tactical tangent. Oh well, maybe some of you will use this advice. Maybe ill start working my slayer rank back up to 35 and not allow friends to play my live account anymore