So, let's get on with my observations:
13th Age is a ROLEPLAYING GAME
13th Age is a roleplaying game, but what do I mean by this? I mean that there are mechanics that involve roleplaying. It is not a glorified skirmish wargame. It is not just about fighting and killing monsters. It is also about who your character is. What is his / her One Unique Thing? What makes them special? Why should the campaign be focused on this little group of adventurers rather than any others? Why do they have the potential to be legends? The skill system has also been streamlined and melded into the background, letting the players decide what their non-combat skills might be as a consequence of what they did before. Hence, 'Pirate +1' can cover a host of things, from sailing and navigation, to chatting to sea dogs down at the docks, plus we know you used to be a pirate in your past, and the GM can bring in elements to the story that could draw on that background. Is that the sound of your old comrade Blind Pew making his way up to the Admiral Benbow inn?
You need to do your homework on your character
Like 4.0, you need to keep focused on what your character can do. Each class in the basic game is like an entire sub-game in itself. I played a Rogue, a Barbarian and a Bard, and each is radically, radically different. Even within each class, there can be builds which can take you off into a totally different direction. There is plenty of meat here for players without the need for additional splat books. But, it means you have to concentrate in a battle in order to maximise your abilities. It is easy to miss an opportunity - if it is not your turn to act, it pays to stay focused on what the other party members are doing and what the opposition is doing. Some characters have out of turn abilities that can react to others' actions. The downside: it is hard to run two PCs at the same time, there is quite a lot to stay on top of. Playing Savage Worlds, you can run a whole squad of GIs quite easily, but not in 13th Age.
A 13th Age GM needs to think on his feet...but players get story input
Icon relationships mean players can align themselves with the great powers of the game world, in a positive or negative way. This makes the game much more political, and gives it an epic feel that is lacking in many games. You feel that what your characters are doing is important, and will affect the delicate balance of power in the campaign world. It also means you can control the story to a degree. I am a fan of the Adventure Cards in Savage Worlds, which do something similar. The icons dice in 13th Age kept coming into play in a big way, helping us to overcome obstacles, find magic items, source help and information and indeed drive the course of the plot. But, caveat emptor, it requires a GM who can think on his feet and build a story on the fly. If you are a GM who likes pre-published material which you can run out of the box, 13th Age may not be the game for you, unless you drop the icon dice mechanic completely, which would be a shame.
Player characters don't feel too overpowered...so far!
We played until our PCs were 4th level. 13th Age has 10 levels, so in power terms this probably equates to 8th level in Pathfinder. At this point in their evolution, I felt they were still being considerably challenged by encounters, and indeed we lost one character KIA at 3rd. However, IMHO, Pathfinder really only begins to break down at around 12th level, which would be 6th in 13th Age. It remains to be seen how the game behaves at higher levels. The spell throwers in 13th Age don't feel as powerful as in Pathfinder, or even in 5.0; hence the game may suit those who prefer a slightly lower magic environment. I reckon you could even run this in a setting like Fritz Leiber's Nehwon.
The Dragon Empire - make of it what you will.
The campaign world is an interesting one. Obviously, the icons play a big part in it, but because it is new and does not have copious amounts of detail, it is easy for GMs to make of it what they will. I think this is a hugely important issue, because the players have more control of the story, and can inject their own ideas into the campaign the minute they dream up their One Unique Thing. You need a world with just high level detail because the players will be re-drawing the map from the start. Running 13th Age in a highly detailed world like the Forgotten Realms could prove more difficult, unless you are prepared to re-write much of the canon.
Battles take less time.
In an average session of Pathfinder, let's say 3-4 hours, you will be lucky to play through three encounters. In 4.0, perhaps two. Battles in 13th Age are much quicker, with the capability to get through 3-4 encounters in an evening with ease. This feels more like the good old days of 1.0, before things got too crunchy. They are still exciting, still challenging, and because of the story driven elements, should still be of importance. Part of this is thanks to the escalation die mechanic, which prevents fights from dragging on, as the advantage gradually shifts in favour of the heroes. Yes, we ran into the odd wandering monster, but most of the time there was a good reason to be fighting the people we were fighting.
Magic items need more work.
I've already beefed about 13th Age magic items on this blog. I'm not sure I like the way they work so far. They are meant to affect the personalities of the character, but really, there are no mechanics in the game to make this happen, and while some players threw themselves into the additional role-playing elements offered by the magic items we acquired, others largely ignored them. Magic items are not as prolific in 13th Age as they are in Pathfinder, and harder to make / acquire. Potions seem to be freely trafficked however, but are less potent given the inherent recovery abilities character possess. My PC owned some elven leather armour which provided him with a +1 bonus, which I could understand - it was elven armour after all, superior to mere human armour. But would it really mess with his head too, particularly as he was a reptile with non-mammalian physiognomy? I have the glimmerings of an idea about how semi-permanent items could be unique and perhaps provide players with some of the abilities of classes not represented in the party. For example, a wand of healing could provide the same ability as the cleric's Heal ability (cf 13th Age, p95), but perhaps with limited charges and usable only once per battle...?
I like 13th Age. Along with Castles & Crusades, it remains the game I would most likely run if the urge seized me to GM some traditional fantasy roleplaying. Is 13th Age traditional? Possibly not. It represents the latest iteration in a sequence of game design which has taken the world's favourite roleplaying game in a number of different directions since the end of 3.5. But it is an important one, and I believe it will hold its own with many groups against both Pathfinder and 5.0.