[Spinner]

I think maybe both the "Planets and Spaceships" as well as the "Kingdoms and Swords" have both been "done to death", as it were. No doubt, these two concepts are the most popular "themes" out there, and historically, the "Kingdoms and Swords" have the lead (look at World Of Warcraft VS Star Wars series, or Asherons Call vs Anarchy Online etc etc etc).
A good "third" should be handed to "WW2" themes, from what I can tell anyway.
But, as someone else mentioned, the question is whether the "theme" actually matters a lot down the line, if the game is good or not. WoW was a lot better (and way earlier) than Star Wars, and Asherons Call was a better game than AO (maybe not more "fun", but certainly more stable).

Also, when it comes to geeky, that's quite "in" nowadays, at least in many parts of the world. However, there is "geeky" and there is "geeky"...
The theme can be geeky, and still have a wide appeal, if it is wrapped up nicely. Star Wars (The Phantom Menace) took in $924,000,000 from the cinemas alone, and if you assume that a ticket is about, what, 7 $ (?), that means you've got more than 100 million potential "scifi-geeks". (I deducted the extra 23 millions, betting there are some supergeeks who saw it more than once)..And it also happens to be about the same as any of the LOTR-movies which could indicate a bit of a tie.
PA has more than it's fair share of "needlessly geeky" features, and one could start at the graphics and interface...
It hits you right as you sign up tbh, that does not look good.
Then it slams you in the face again, as you get your email containing the password...In plain-text black and white...
I get spam that looks more interesting than that.

Then you get into the game, and end up at the overview screen, which is red and blue, with white text..And a header containing nothing useful, just the logo and the name of the game. Apart from the tiny bit at the bottom, thats it when it comes to graphics here. Tables, border and plain text. Now, you can spend thousands on advertising for PA, but the GUI and design alone are quite big turnoff-points when you compare it to other titles. And this is where any new game can pick up a lot of points in competition with PA.
Now, I won't go into the "information" in the game, but the mile-long overview I got now as a new user, with various points to distribute for resources, research and constructions, with no clue or tooltips explaining what any of that actually means, the user-friendliness is plummeting towards zero quicker than you can spell the letter P...
No worries, I am more than willing to take the blame for most of this, as my original design also left things to be desired...but a lot of time has passed since this was designed, and the net itself has changed a lot. Back in December 1999 we had to cater for modem-users on the other side of the world, and that just isn't needed anymore. Not modernizing the game kills it off, with every passing month...

My point with all this, is that you can't use PA as a measure of the genre at all. Ogame has shown that the genre is alive and kicking, no doubt of that, and that the "space" theme is very suitable indeed. PA has shown that all good dinosaurs eventually die if not cared for correctly. Nobody plays Pacman in the arcade anymore, and here in Norway, the arcades are pretty much all gone while gaming is happening elsewhere.

I'm pretty sure the theme is not paramount to making a browser-game, as long as the game is nice to look at, has a nice GUI, buillt-in information without forcing users to read a manual and , of course, the game is fun!

Thats my 2 eurocents anyway.