Classical is about raiding, building an army, and building an economy. You can usually avoid one of these three if you excel at the other two. Egypt and Hades does well defensively as they can build an army and an economy together due to their defensive nature (and cost of thier military units). Norse and posieden are good raiders, which sets the pace for the game. Zeus is not as good as posieden at raiding, and not as good at hades as building an army with an economy.
But the fact is, Zeus has been competative in the past, and of course, once people recognize the futility of Hoplite armies (IMO, mainly because they suck vs thier counters and can't counter what they are supposed to effectively), they will become competative again.
god bonus' are what distinguishes civs so we need to look at those as militarily the hoplites are no better than anyone elses (weaker given minor god choices). Bonus damage to buildings can be nice, but not a game changer, if your attacking buildings, it means your not in combat and therefore the building would fall anyway. Its like the arguement about norse buildings being weaker, its irrelevant as a building is going to die if it has 2100 hp or 1600 nearly as fast, but always and only in the same situation, when unguarded. Faster hoplites is in best case scenario decent, although most games pretty irrelevant; norse have faster infantry accross the board and I don't hear many people touting the advantage. This leaves bolt and favor generation.
Bolt is great as the experts are showing. I used to think it was great to bolt that scout when I saw him, but now I realize that its so easy to just pop out a pegasus to replace it. Good use is bolting an early villy, pharoh, or ulfsark. It can really mess with the early game if successful.
The other advantage is favor generation. There is one time when it is useful, and that is early classical. Being able to pump out two centaur right away and pick away at the norse paper tiger economy is extremely important. If you can kill 5 villies, many norse can't recover, and more importantly, they end up countering your raid.
I'm not sure how useful the additional favor generation is past 8 minutes as one more villy on the temple by either other greek will give you as much favor as zeus.
Naturally, mythic is all Zeus with myrmidons being the most powerful unit in the game. But then, how many games are decided in mythic?
So if your not effectively using bolt, and not raiding with centaur right away, then your better off with one of the other two greeks; they can do anything Zeus can do and better.