Empire Earth was the most expansive rts and most innovative when it came out (before AoM, Rise of Nations). It does expand into the future with nanotech and the like, but you can limit yourself to the earlier ages if you want. I'd say if you wanna stick in the dark ages I'd go AoE 2 with the conquerors expansion as it is pretty much the best, although it will look kinda old now. I wouldnt go all the way back to Warcraft2 the interface is so limited, even starcraft was lightyears ahead (not just in gameplay). The other problem with Warcraft2 is the rock/paper/scissors everything has a counter thing wasnt really introduced yet. So it's just rock v rock and you all have identical units pretty much. War3 is much better with more variety, though many are annoyed by the unit limits. There are a lot of new RTS games that are really horrible such as the lotr one and another one that basically tried to copy Warcraft3. Stick to ones mentioned in these posts. The other thing you could do is check pcgamer to see if they have reviewed it. If a game is bad they will definitely tell you. Not only that they rate the games on genre not on an overall scale.
Oh yeah AoM's best feature is the myth units not necessarily the god powers.