This is a discussion I have been involved in basically since Blood Angels dropped. This is going to be a part I post, with a follow-up post to more fully elucidate on my thoughts on jumper armies.
As background, recall back to those awful PDF days. With the advent of True Line of Sight, Jumper armies were kind of given the shaft, due to not ever being able to get completely out of line of sight from the opponent as you tried to get across the board. Combine that with a woefully inadequate amount of melta-weapons (or decent wargear options for the Assault Squads at all, really) and the army just kind of sucked. You got shot to pieces by players with balanced lists like Stelek's original "Best of Space Marines" (this is the classic 3 MM Dread, 3 Dakka Pred, MM Tactical squads in Rhinos, etc). The opponent simply had too much anti-infantry firepower, and you too little defense against it, to survive. Add to that the fact that you had to get your enemy out of their bawkses first, and you were really up a creek. To add insult to injury... you really weren't that scary in close combat.
