I'm a platinum player so I can only speak from that level of play, but all of these changes sound awesome. SC2's strategies do still change but they're becoming stale, especially as a Zerg player. It sucks not being able to hold any ground at all unless you already have a supply advantage anyway. The swarm host in particular helps offset the ridiculousness of the baneling being our most effective low-tier counter; it's stupid that our counter to T1 is a one-use suicide unit that costs gas and takes twice as long to train as other units in its tier. The swarm host will be reusable and burrowed, finally allowing us to defend ourselves AND be offensive, like siege tanks. We'll be able to afford some strategic mistakes in the early and midgame. And I can't say enough good things about the viper. I'll definitely miss my changelings though. I hope this brings SC2 closer to the depth of Brood War.
Can't wait to play this. If it were available today I'd drop $60 on it in a heartbeat.