(Note that I still haven't played the game. Let's see if I have a chance in the weekend, though after reading through the Essen reports of various friends I have several other games I will prioritize above this one.)
Okay, it is good. Possibly really good.
I did not play it myself during the Con in the weekend, but that was purely because there are so many copies of Nations available in the local clubs I play and people were so enthusiastic about it that I will have plenty of opportunities to play it to my heart's content during the following weeks. A lot of people who are big fans of Through the Ages (including also guys who play it competitively) and other games of similar scope (say, Terra Mystica, Eclipse etc) liked it a lot and many of them played several rounds during the weekend. I listened through one rules explanation and the game certainly sounds almost like a clone of TtA in terms of concepts, but seems to play differently enough. It also seemed to work quite well with 4 players too, in contrast to TtA that is purely a 2-3 player game when playing live.
The reason I didn't want to "waste" my time with Nations was that during the Con there were several new Essen releases that will be harder to find in the future, including some esoteric Japanese cards games etc. The best of the new releases I tried were perhaps Concordia, Prosperity, Yunnan, and Russian Railroads. Rampage was another hit, but it's maybe more a fun toy than a game. The low-point of the weekend for me was Packet Row; I can't imagine people actually release that kind of stuff anymore.
Edit: Some more comments about Nations. One strong point is that the rules are much cleaner and easier to explain compared to TtA. The biggest issue some people commented about was rather high degree of luck in terms of the event decks. The event decks are large but only two cards of each type will always be used in a single game. Furthermore, some of the events are very cruel, whereas some others don't do much. If one tries to play the game with low stability or military they will expose them pretty much to the luck of draw; if some cruel event related to that category comes up then they are screwed, but they might just as well luck out and go through the whole game without ever needing the track for clearing events. More generally, the card distribution seems to cause huge variance, making the game very tactical instead of strategic. It seems one cannot decide in advance things like "I will concentrate on the books/stability/military/whatever in this game", but instead one needs to really adapt to the choice of cards. However, you do not see the cards of the future ages so you can only hope that the tactical choices you made during age X will still be valid during X+1.
As a practical example of the variance, someone tried focusing fully on the books in two different games. In one game they managed to reach less than 20, in another game 75. In the latter game people not even trying to maximize the category reached more than 40. Apparently that focusing paid off a lot more in one of these games, and it was purely determined by luck of draw.