I actually thought DMR bloom was a very good and clever mechanic. As opposed to H4 where it does sort of come down to who sees who first (ala CoD) in Reach both opponents have a fair chance even if one does get the first shot. Because bloom makes it more difficult to kill it required more skill, therefore Reach DMR's are much more interesting than H4 DMR's.
Bloom slowed down precision weapons, which made spray and pray more effective while slowing down the gameplay for no good reason. In mid to close quarters battles it became random, a person could spam and get lucky, so everyone HAD to spam.
Power weapon almost always win but in every other Halo people have a chance to overcome certain power weapons with precision weapons. Bloom, negated that. Simply because it slowed down kill time so much.
It's a terrible mechanic for Halo and only people who liked it are the people who suck with precision weapons.
My sarcastic tone doesn't translate over the Internet, which makes me sound like an ass. Usually I mean no offense.