Well I doubt that the people complain because they don't like the era. I loved TW, with Rome and Shogun being my favorites. I bought Empire and was hugely disappointed. And Empire surely isn't my only strategy game playing in this era. It simply lost flair compared to other parts of the series, it had serious flaws till 1.5 and some still remain and are only fixed by Darth Mod and others.
Than there are promised features that never made into the game. But what annoys me by far the most (no, not Steamworks - I'm fine with that): their crippled (better said non-existent) support for mods.
Hell, I don't keep Rome and Medieval 2 on my hd, for playing vanilla! It's all about the mods. When CA will still abandon those developers with Shogun 2 either, I simply won't care what else they do with the game.