Economy
Out of the three races Zerg has the strongest macro mechanic. They can expand the fastest and create the most workers. So it was generally understood that in the early-mid game the Zerg should have a stronger economy than the Terran player. I remember the general rule of thumb for Zergs was to always be one base up on your Terran opponent. This was what made Ling/Bane/Muta vs Marine/Tank such a compelling engagement. Zerg wasn't supposed to have cost efficient trades with Terran armies, in fact if they could just trade evenly they would be coming out ahead in the engagement. This was when Zergs could overwhelm Terran armies with just sheer numbers. Mutalisks were used to harass the Terran economy as much as possible, picking off SCVs/tanks/medivacs whenever it could. Also engaging on creep for Zerg was so important which made creep spread very critical when trading with Terran armies. Now with the current meta game in ZvT, Zerg can now trade cost efficiently/evenly with Terran in the early/mid game with the new Queen range and infestor meta game and in the late game Broodlord/Infestor trades very efficiently with almost any Terran army. Because of this the match up was been reversed since Terran can't really engage cost efficiently in any part of the game currently. Now Terran needs to have the superior economy to Zerg, this why fast 3CC builds are so popular now. In the current meta game I feel as though the Terran is behind if they're not one base up on the Zerg. This doesn't make sense to me since Terrans can't expand nearly as quickly as Zerg can. Perhaps I'm missing some intricate details but I don't think Terran and Zerg were meant to be played in this manner.
Unit Compositions
About two years ago Zerg was known to be the "reactive" race as in it's unit compositions were always dictated by the Protoss/Terran unit compositions. With good creepspread, Overlord placement, Overseers, and changelings Zergs could easily identify mid game/late game army compositions of the opponent. It was up to the Zerg to react correctly to deflect the up coming attack. Now in TvZ since the infestor is useful and cost efficient in both the mid-game/late-game against any composition, the "reactive" part of race has completely disappeared. Infestors can be used to deflect any mid-game aggression from the Terran and yet not have to devout any significant resources to tech switching units. This has caused another role-reversal in the TvZ matchup. Terrans have now become the reactive race in TvZ. Since Terran doesn't have a significant advantage (cost efficiency wise) in the mid-game anymore Terran players have to react to Broodlord/Infestor, they have to react to Ultra/Infestor. This also doesn't make sense to me. Terran of all three races has the hardest time changing tech paths and Zerg has the easiest time of changing army compositions.
Early/Mid/Late game
I'm completely lost on this topic. In the current meta game I have no idea where the transition from early to mid to late game is anymore. Before with the reactor hellion expand builds Terrans would have early map control to deny a third base before mass Speedlings or Mutalisks would regain it control to safely take a third. In the mid game ling/bane/Muta vs Marine/Tank were the standard army compositions, only if Zerg came out ahead in the mid game would they be able to safely transition into a Hive Tech army which took a while since infestors were needed in their army composition. A popular build now is the reactor hellion/cloak banshee into 3CC which doesn't really have the same affect since Queens are so dominant to keeping away harass. I see Zergs getting Hive as early as the 12:00 min mark, and then Terrans attacking with a maxed Marine/Tank army at around 15:00 mark before Zerg's Hive army really kicks in. So often I see Terrans kill one or two bases before getting rolled by a just spawned Hive tech army. Mech is starting to get popular in TvZ but you can't really move out until your maxed, again it's that hit them before Hive tech mentality still. So what is the early/mid/late game right now?
TvZ was and still is my favorite match up to watch and play, however I feel I have no idea how to spectate it anymore. Base counts don't seem to matter. Worker counts don't seem to matter. Creep Spread don't seem to matter. Supply counts don't seem to matter all that much. All of these things I stated don't make sense to me in this I wish I could because I love TvZ!