I've got a lot of criticisms to make, but, so it doesn't seem like I'm just slating your abilities, I should say first of all that you're not that far off being a useful player. The stuff below is mostly very easily addressed, and, most importantly, it looks like you already have a solid grasp of many of the key elements of the game.
Okay. Brace yourself...
1) Resources not improved
2xClams (food!), Furs (happiness!), Copper (!?!)
You've now teched IW and mined the Iron, but why didn't you claim the Copper as soon as it showed up?
2) Not enough exploring
You should've explored further early on, but even if that wasn't possible you've now got Open Borders...
3) Settling one tile from coast
Settling one tile from the coast (as is the case for your capital) is usually a bad move (mainly because you can't build a lighthouse). But when Clams are one of only two food resources in the city radius?
I see you settled in 4000bc, but did you settle in place?
If so, and you couldn't see the clams, then it's a mix of bad luck and inexperience. You should be able to see quite clearly when there are sea tiles just inside the Fog (especially when there's a river running into them), and so you should always explore that direction before settling.
If, on the other hand, you moved from the coast to where you settled, then it's a very
move, I'm afraid.
4) A lot more workers needed
Waiting for three workers to improve a whole empire will slow your game down immensely.
No less than one worker per city is a good rule of thumb.
This is also an important reason why food-heavy sites (inc. that sheep/corn site to the west) are so incredibly valuable early on: food bonuses = faster production of workers (& settlers, of course).
5) Use your civics
You've only opened up Slavery, Caste System and Organised Religion so far, but you've yet to adopt any of them.
With judicious use of the whip (combined with that food thing I mentioned before) you could have had more troops, more workers and/or more buildings by this time.
Alternatively, with Caste System you could've saved yourself building monuments everywhere (by using an Artist specialist until the border pops), and sped up GP generation by running Merchants and/or Scientists. (Again, more food would be necessary to take full advantage).
And, with OR, you could've spammed missionaries to boost your shrine income (and convert other civs - see below), and to speed up production of the buildings you need.
6) A different state religion to everyone else.
Unless you're so powerful you can afford to ignore diplomacy altogether, this is a MASSIVE problem. Either stay without a religion, adopt an AI-friendly religion, or try to convert a couple of other civs to your religion. Otherwise you are doomed to end up as the world's whipping boy.
7) Too much tech, not enough development or military
You're building your house on sand if you tech as fast as possible with little or no regard for the development of your lands, your cities, and your military.
You have way too many unimproved tiles, too few buildings in many of your cities, and far too weak an army for this point in the game.
With such a weak basis, it's no surprise that your early lead quickly evaporates, and you present a tempting target for the AI's units.
Which leads me on to the final, most important point:
For each and every decision you make, always ask yourself: "What am I actually trying to achieve here?"
Fast teching alone is pointless if you never take advantage of the techs you research.
Strong empires win games, and getting the techs required to take your empire up a notch is, of course, one of the keys to building a strong empire. But it doesn't look like you've paid much attention to leveraging the techs you've researched to strengthen your empire.
Normally, I'd assume that this was evidence of a lack of strategic planning, but it does look like you have a fairly coherent strategy going on, despite the problems I've listed.
So I'm thinking that maybe you have a variation of the old "buildoholic" syndrome. But instead of the typical "I must build every building" mentality, you seem to want to research every tech as soon as possible.
Many of the issues listed above could be dealt with quite easily, provided you can value techs by the benefits they can give to your empire, and strive to maximise those benefits, rather than shooting off to grab the next tech as fast as you can.
Hope some of that helps.
Edit: Wow, I didn't realise how much I wrote... Sorry for the essay.
