You're right that season two was too short. Book two was a longer book, and it really could have used another few episodes to cover everything it should have covered. That was too bad, but I suppose budgets are what they are. They have a pretty generous budget already.
But the good news is that book three will be split into two seasons. This next season will cover roughly the first half of book three, and it will end with an iconic scene that takes place around the middle of book three... those who have read the books know which scene I mean.
As for book four... yeah, it was kinda disappointing. But for those who don't know, a big reason for this was that book four didn't cover a lot of the main protagonists at all. That was because book four had gotten so long that Martin literally cut out half the viewpoints and moved them to book five, so that book five almost became like like book four, part two: a lot of book five takes place at the same time as book four, just with a different character set in different places. For this reason, it's a virtual certainty that the TV show will weave books four and five together, and possibly start taking even more liberties to make it all mesh correctly.
What I'm really wondering is what will happen when HBO has covered all the material Martin has written. It took him five years to write book four and six years to write book five, and as Martin plans to write two more books, it seems safe to assume he won't be done with them by the time they've finished filming the existing novels. I'd imagine HBO will simply be forced to stop and leave the final books unfilmed. Hard to re-assemble a cast and crew after a years-long hiatus when most of them will probably be committed to other projects.
EDIT: BTW, book three is the best book by general consensus, so I'm hoping this next season will be even better than the others. I'm particularly looking forward to the Jaime-Brienne and Daenerys storylines.
