Let me preface this by saying that AoWIII is a very polished game; it looks quite nice, has few glitches, and it seems like the Devs put a lot of thought and work into this game.
However, I cannot recomend it. Why? It's simply not an enjoyable experience for me. Now, don't get me wrong: I've always been fond of TBS games. I loved Civs 3-5, and have played quite a bit of Fallen Enchantress, as well as some Galactic Civilizations. I'm acquainted with the genre, but am by no means an aficionado.
So, why don't I enjoy this game? Well, a large part of stems from how narrow your in-game options are. There are plenty of choices between class and race, and those choices feel significant enough, really, but once you actually start playing the game, you realize that there's really only one way to win: expansion and conquest. I knew going in that this game would be more heavily conflict oriented, but to the point where that's the only means of victory? Not exactly what I had in mind, though I can certainly get by with that.
But it's not just that you'll have to go to war to win. It's more holistic than that: everything in this game is about conquest. The only real purpose of your cities is to produce soldiers, in some form or fashion. You build buildings to unlock units to fight wars. You conduct research to unlock units to fight wars. You manufacture "merchandise" to fund your wars. You "build housing" to increase your domain to capture "resource nodes" (that only provide a slight buff to production rather than serving as actual resources) to more quickly produce units to...wait for it...fight wars. Now, fighting wars isn't necessarily a bad thing. The combat is very well designed and has a good deal of depth to it, especially when you take into account the racial and class distinctions. But, this generally superior combat seems to come at the cost of the depth of everything else.
And that's just the problem: this game lacks depth. There is no real economy management, no real resources to capture (the only two "currencies" are gold and mana, the former of which is over abundant and the latter of which is often too scarce), and no real tech tree to navigate. You just plop your identical cities down to increase you GPT to support a bigger army. There's nothing else to it. You don't have to worry about acquiring special resources or developing advanced industry to train particularly powerful units, you just unlock them via research. And you can complete that research very quickly (late game starts at around turn 50 in a standard game, though the overall pacing can be sped up/slowed down during setup). By the time you've done that, you've rendered most every other standard unit in the game obsolete. You can really spam your way to victory against the AI (assuming they're not doing the same; otherwise you just get caught in a gridlock). And so, you lose that depth again.
If you love TBS combat, you'll probably enjoy this game. If you're looking for something more well-rounded, consider picking it up on sale. If you're expecting something akin to Civ V, check out GalCiv III (maybe; it's really expensive and still early access).
ADDENDUM 1: Since patch 1.093 (I think), pacing has been slightly improved through the addition of new production-related buildings and other changes. However, there have been no major changes made to the other mechanics, so, take it for what you will. Mana has been capped as well, which helps to prevent surpluses. T4 spam is still prevalent, though it occurs about 20 turns later for non-summoning classes.
ADDENDUM 2: Since patch 1.12 (or something, I dunno), different races have received different buffs/nerfs, and different gamespeeds have been added. This does indeed help with pacing, and provides more strategic depth to the potentially longer early/mid-game. However, economy and diplomacy are still pitifully simplistic, meaning that my core issues with the game (the near single-minded focus on combat) remain. The late-game is still shallow, even when opponents are on fairly even footing.
ADDENDUM 3: A new expansion has been announced, Golden Realms (I guess? Heck if I know.), that adds a new shorter campaign and race. It's Halflings, and it's only three episodes long, compared to Vanilla's 6? So, basically, it's half-sized, just for the Halflings. It's pretty clever. More importantly, (to me, anyway), it's supposed to bring a lot more to the table in regards to empire management, like special, competitive city projects, new, powerful effects for "special tiles" like treasure sites, and exclusive racial defensive improvements. A new victory condition has been added, as well. Unsure as to what they'll be doing with diplomacy. Iffy on the price, too. Something to think about, though.