So Heir to the Throne just came out, and looking at the features, there isn't much. Each expansion is like $20, and often require previous ones. I simply wanted to buy In Nomine, supposedly (and byt he features) regarded as the best, but looking at the price of Napoleon Ambition's too was simply too much. Any thoughts?

Any chance you could wait for a "complete" edition?
I assume this is unlikely any time soon, if they're selling expansions for $20.
I've never played the game myself, so wouldn't know whether that's an outrageous amount or not.

Yes, people buy them. And yes, they're definitely worth the asking price, IMHO. It may look like they don't change much, but they do - more than a lot of other expansions I've seen for other games.
BTW, you can buy EU3 with the two previous expansions (Napoleon's Ambition and In Nomine) for $16.77 at Gamersgate:
http://www.gamersgate.com/DD-EU3COM/europa-universalis-iii-complete
You get the original game plus 2 expansions for less than the price of one. Great deal, if you ask me.

I bought both In Nomine and Napoleon's Ambition not long after they came out. I agree that paying $20 each in addition to the original game is a bit much, though I didn't really mind because they are not only expansions but also substantially improve the core game, especially IN, and because I think Paradox does a phenomenal job supporting their games which are, after all, niche products that don't sell millions of copies. So I'm happy to pay them for their hard labor.
In any case, by now you can buy the complete bundle for far less than that. For example, as someone pointed out yesterday in the "game deals" thread, Amazon has EU3: Complete, which includes IN and NA, for only $7.73!

I already have Eu3, and am thinking it might be cheaper to buy the complete edition that the expansions!

Definitely pick up the expansions...they change a LOT. And while Heir to the Throne might not seem like much, a major change to the Casus Belli system, increased Holy Roman Empire options, improved options for merchant republics, AI tweaks to make better use of diplomacy and be more cunning, etc. make HUGE changes to the game.
At the very least, pick up the Complete Edition to get NA and IN. IN improved the game immensely.

i got eu3, napoleon, and in nomine. i'll be skipping this one becase i think having bought 2 expansion packs i supported them enough.

I will wait for the MMP team to release a HTTT port to MMP.
Hi there, Panther :) Sorry for the failure of the Venice SG :)