As if the show needs any improvements, it is already epic in it's own right.
Here are some improvements, I would like to see in future seasons. You could call them, wishes, but it for me, in my opinion, I would like to call them improvements.
1. FLASHBACKS! I mean, I know the book was POV, linear, but it did give background stories through conversation. This does not mean the show can not show a flashback scene to show an important event that ties into the story, kind of like a prelude to the beginning of each episode maybe? A scene I would love to see is the Rhaegar seducing Lyanna Stark at the Tourny of Harrenhall! This is probably the event that started the rebellion! This is like the Romeo and Juliet story right here in Westeros. Rhaegar and Lyanna secretly but obviously in love to rival families. We can get the answer as to what Ned promised to Lyanna when she died! Plus we would get Sean Bean back to play Ned hopefully!
Flashbacks, why not! This is the TV Show, not the book, there are 100 other things different from the book. Why not flashback scenes!
2. Spin offs, events that happened before the series started! Maybe George doesn't finish the books by the time the show catches up, a spin off would help stall.
3. More episodes. Any number over 10, even if it is only one more. If True Blood has 12-13 episodes, Game of Thrones should have 25.
4. Strong Belwas.
5. Me casted as Dany's king.
1 - I hear what you're saying; even the earliest focus groups they asked said they think that Rhaegar, Lyanna, and the others involved in Robert's Rebellion would be more effective in flashbacks than just people talking about them in the present (in a sense, I guess, the "Complete Guide to Westeros" motion comics do give those, but many ignore them and only focus on what airs on HBO). Even in the pilot, there were flashback scenes filmed of Mad King Aerys II Targaryen killing Rickard and Brandon Stark, but they were later cut. So there's a massive debate among the writers about when or if they should ever use flashbacks.
2 - Actually, they have considered making spinoffs based on the "Tales of Dunk and Egg" prequel novellas which are set 90 years before the beginning of the series. but that leads into point 3:
3 - The cast and crew, writers, everyone, has said that they physically can't make more than 10 episodes a year. Even with price as no object, ignoring all costs, they physically can't write, refine, act, and edit more than 10 episodes. Otherwise there would be a massive drop in quality. Yes, they're not just "making it up as they go along", it is a book adaptation and the story already exists, but they physically can't produce the adaptation faster than this.
No we don't want to race ahead and make so many episodes we catch up with the books (haha), I assume you mean "adapt the second book with 20 episodes instead of only 10, so we don't lose any plotlines" -- I would have enjoyed this too. But I understand and fully agree with the writers' and production teams' insistence that they PHYSICALLY CANNOT make more episodes than that in a single year.
...of course, they could have adapted the second novel in two HALVES, each of 10 episodes, but aired across two years....but that would have taken too long I guess. They did split book 3 in half, but that's because it's about 50% longer than the previous novels - which thankfully meant that much less was cut out this time (they did cut Edric Storm but he was cut from season 2 so I understand they had to work with what they already had, and as for cutting the Brave Companions, they weren't really "cut" so much as streamlined...)
But in summary, they physically can't make more than 10 episodes a year or there will be a drop in quality.
Look at how bad mid-2000's shows like Lost, Heroes, and Battlestar Galactica turned out when they started trying to crank out 20 episodes a year - it's one of the major reasons that BSG failed (hypocritically, even though they switched to 20 episode seasons from Season 2 onwards, they'd still air them in two halves, six months to a full year apart - in which case, why not just swallow your pride and call them "seasons"? (because the network has to pay them more if they're separate seasons). Ack.
They have discussed making prequel spinoffs based on the prequel novellas; however, they said they'd only consider making them once the main TV series is finished, because their hands are full making "Game of Thrones". But after Game of Thrones ends (hopefully, at Season 8, if one season equals one novel, plus another because they split book 3 into two seasons)...after Game of Thrones ends at Season 8, we'll continue on with the "Dunk and Egg" prequels. But they cannot possibly make them simultaneously.
4 - Indeed, need more Strong Belwas. There's nothing outright preventing him from just showing up in Slaver's Bay in a later season.
1. I would love to see like a spin off called "Valyria" where they show the Targaryens and other houses before the demise of Old Valyria! Who says they can't do it simultaneously with separate producing groups?