I'd say it depends heavily on who's your healer. If you're running with a priest, stoneform is huge. Go with a druid, and it's not such a big deal. It's still nice ofcourse when you have a rogue on you and your druid is CC'ed, but for 2v2 with a druid i'm not sure i'd prefer stoneform over shadowmeld. 2v2 with a druid involves alot of drinkfest and shadowmeld is actually really nice for that.

It was a big nerf towards keeping large amounts of the enemy team hamstrung.

Well, Hamstringing 3+ people at once and not having to worry about it is overpowered, so I suppose it is huge unless you look at it from a balance standpoint. You can still keep 1 target hamstrung pretty much the entire fight and another person hamstrung 2/3's of the time by intercepting and Hamstringing. Sorry to any warriors who thought the old version of Hamstring was in any way balanced. I don't think there should be any spammable snare in the game, so in my opinion it is still completely overpowered.

It's huge in that hamstring can now fall off during short CCs. At 15 seconds and people spamming it I'd rarely if ever be out of hamstring an entire match. Now it falls off quite often if I'm able to shake the warrior for a couple seconds. It was a HUGE change for certain classes.

It means a few important things, 1) hamstring's duration is no longer the same as the cooldown on intercept, 2) Wing clip and hamstring have the same duration, and 3) it makes it more difficult to hamstring multiple people at once. It means a smaller window for warriors to spend GCDs on damage, because if you repeatedly wait until hamstring has 1 or 2 seconds remaining before you refresh it, good teams will take note and apply any short duration CC they have to let the hamstringed target get away.

Hamstring also does not have a 100% success rate, particularly against hunters, whom it often takes many GCDs to apply hamstring to. A smaller duration on hamstring means it's more likely to fall off due to the warrior being stopped in some manner. This doesn't have to be "standard" CC like sheeps, I'm talking short duration effects as well like scatter shot.

Hamstring is also not free. It's low cost, but not free. Shortening the duration increases the amount of rage you need to spend refreshing it. With a 15 second hamstring, it was trivial to have enough rage to keep both MS and hamstring on somebody since you did not need to refresh hamstring very often. Now, with a 10 second hamstring, you need to spend more rage refreshing it more frequently since it reaches the 5seconds remaining window of where you can be short-term CCed, allowing hamstring to fall off and your target gets away. Against any target with roughly the armor of a hunter or higher, this is by no means a given. This is also in the complete absence of power word shield I might add, which makes the rage generation situation god awful.

Basically the hamstring duration nerf vastly increased the number of windows where it's possible to stop the warrior for a few seconds allowing his target to sneak around a corner and lose hamstring and gain a bunch of distance. That's why it's a big deal.