In complete overall honesty;
I'm a Halo 2 fanatic. The ranking system was at optimum level - even over Halo: Reach. Reach is an individualized game where it's every man for himself. You get players that either, "Yoink!" or have others work for the kill, then when they die, take that kill. Playing as a team, and working with other people, such as clans, (which was a HUGE thing that they got rid of - goodbye KSI and other trivial clans) and was definitely harder to level up.
The major reason why people stopped playing Halo 2, (or kept playing) was because of standbyers, hackers, and what not. Why not keep Halo 2 going, with better graphics, the system they use now, and the same weapons as before. Although, I do like the new extra things, such as; sprint(!), evade(!), jetpack, armor lock, etc. and it tricks my mind knowing that Halo: Reach was before Halo CE, and yet they don't have them anymore. I know they pulled the Star Wars thing, where they did the prequals after all the old movies had been made, and it was a fantastic idea, but now they should update the originals with new versions.
I haven't played in any tournaments, but have played with MLG players and have been able to hold my own, (in all modesty, lose by 10+, with a K/D ratio of -5). Haha. It took skill in Halo 2. The snipers didn't have a delay, like they do in Halo: Reach, and they did have a few button glitches (BxR, double/quad-shot, etc.) but I think now they can remake all that and make sure that everything's the exact same. Same maps, and same materials/locations, everything, just better graphics.
I have faith in you Bungie to make the right decision!