Terrain Matters. Many people decry the lack of depth or moan about how the Tactics in Age of Sigmar are too thin to allow for any kind of challenging game, and it all boils down to dice rolling in the blob that inevitably forms in the center of the table. While I disagree, and have been writing Age of Sigmar tactical articles for a little bit since the release, one of the easiest ways to add challenge, tactics, flexibility, and variables into your game is to make good use of terrain. The general with a better understanding of how to exploit it will be more likely to win, and the games will be more engaging and require different actions based on the nature and placement of the terrain you have. Simply put - if you are blobbing up in the middle and having one massive brawl, the simplest way to fix that is to put a lot of terrain on your table to force players do do something other than pile up in the center.
Physically speaking, you can't have a blob in the center if you put a bunch of walls, building, or forests in the way, but there are also reasons from a tactics standpoint that terrain will increase the enjoyment you get out of you games of Age of Sigmar. If you are a combat heavy army you want to use terrain to provide cover bonuses/block line of sight to advance. Additionally when playing another combat army you have to decide if the cover bonus is worth launching an assault in to cover for of if you'd be better off with both units at no bonuses. For shooting armies you want to be able to command firing lanes as well as using other units to block and force units into shooting lanes. Even if you are ignoring the rules for special terrain and using only area terrain +1 armor save as 'cover', your games will certainly change based on who controls which hills or ruins. Preventing an enemy from charging you or shooting you based on positioning, or funneling their charge into your anvil unit because of a corridor of terrain benefits players who can set this up and definitively requires some tactical ability to be able to capitalize on these opportunities while denying them to your opponent.
Regardless of what type of terrain you are using, if you take a wizard or two you will find that combining mystic shield with sitting in terrain gives a +2 to your armor save for the unit. For super tough 'tank' units this takes their 3+ armor save to a 1+, so they can only be hurt by mortal wounds or things with rend. Depending on your situation, this will win you games because of a virtually unkillable unit. If nothing else, it will force your opponent to direct mortal wounds and rending attacks in that direction rather than somewhere else, or give them a priority to unbind spells or kill that wizard, and any situation where you force your opponents' hand is beneficial to you if you can make use of it.
From what I'm hearing part of the growing pains people have been having with AoS is playing games on similar boards to 8th Ed (quite sparse on terrain in the center so those hordes have room to move), whereas it seems to benefit from more terrain-heavy tables. Not zone mortalis/cityfight or anything, just like what 40k is (supposed to be) played on. remember, you can roll for terrain, placing 1-3 things per 2 foot square. On a typical 6x4 foot board this means 6-18 pieces of terrain, and those can have special effects if you want. Gone are the days of a building here, a forest on your opponent's deployment zone, and maybe a hill off to the side, now we're meant to play in more dense environments.
Additionally, if you're playing with Sylvaneth figures, some of their models can currently 'spawn' woods that very much help them accomplish their tasks. These can allow for teleporting in a sense, block line of sight, restricting charge lanes, etc. It looks like they are the kings of terrain for the time being, because particularly with the Sylvaneth Wildwood they can cause all kinds of headaches for their opponents with magic restrictions and a constantly changing landscape. If You want to dive heavily into the terrain aspect of tactics, I'd suggest taking a look there.
How have you been able to make use of terrain in Age of Sigmar? Has it swung the balance of any of your battles so far? Let us know!