all i know is, Space marines really need an update soon
Tac squads= not so tactical and use up to many points for less than effective return due to newer armies getting more and more AP 3 weapons and newer armies getting more and more shooting.
Guard= orders for double or triple shots, enough flashlights more than brings down space marines
Greyknights= Can have Str 5 storm bolters plus twice as many heavy weapons as a tac squad
Dark eldar= poison weapons and lots of AP weapons, let alone more heavy weapons
CHoas= depending on dark gods, they are either faster, tougher or just plain better in melee than tac squads+ still can shoot
Dark angels= Cheaper and better options and if i remember, dont need to be a 10 man team to get a single heavy weapon
As for HQ's space marine codex is so far behind on normal and named characters. Their cost and effeicentcy for one is lacking compared to other armies. The same goes for a few of their units.
Assualt/vanguard marines= Just about no codex space marine player fields these any more because if you want jump back melee infitry, you just play blood angels
Terminators= not much played anymore either because now of better options in greyknights, space wolves and dark angels. They are still good, but just being a few points cheaper with nothing special compared to the 3 named before just doesnt drive a selling/playing want
Landspeeders= When was the last non-dark angel player you've seen use one? the reason is because they are to expensive and die to sneeze. Granted 6th edition gave them a cover save for moving, it more or less doesnt help from mass shooting and now with flyers to take up fast slots, whos going to use them?
Techmarines= Besides an thunderfire cannon, no one uses a normal tech marine with servitors
Tanks= rhinos and razor backs are still good for what they due, predators are a bit expensive and need to be kept in cover now, landraiders are not even worth taking. to expensive and with new 6th rules, 4 glances and its gone. Vindicators are still decent but nor widely played and then we have a whirlwind which just about no one uses