I've probably played a hundred games of St. Petersburg, and I must say I still love it. It's got a few flaws, like everything, but it's by far a favorite of mine and many of my friends. Since it's such a great game, I thought it'd be worth me telling you why you should consider playing it if you passed on it in the past.
Like Puerto Rico, St. Petersburg has a trade off between needing to build income early on, and focusing more on points later on. Also like Puerto Rico, you have a few strategies, such as going for buildings or aristocrats, which you can pursue and blend. One big improvement St. Petersburg brings is that the cards and what your opponents choose can force you to have to adapt your strategy sometimes. This is great for keeping you on your toes.
Because money is so tight in the first 4 rounds, there is often excruciating discipline you need to exercise. In a 2-player game, where this game excels, not exercising that discipline can lead you to implode in a catastrophic way. It's pure awesome in a game once you know the land mine is there!! No other game forces me to hold off on performing an action for 2 rounds so I can be sure I'm going to have money to buy 4 workers laer. And then, sometimes, after starting to hold off, the other player can do something that forces me to change direction again. It's a great interplay.
That being said, 4 Player with this game is a bit Squirly. It's quite often you'll get to choose workers, the staple income generator of the game, 4th and 3rd in the first two rounds. This results in a somewhat minor, but immediately set back. In a 4 player game the number of rounds is also shorter, so this limitation is magnified.
Another weakness is that a few of the cards are also a bit overpowered compared to the rest. Many of the most powerful cards are pairs in the deck, which means in a 3 and 4 player game you won't get them by luck of the draw. In a 2 player game there is generally an opportunity cost to taking a second card which evens this out, since having 2 mistress of ceremonies or 2 observatories isn't such a great boon.
Still, these flaws are minor enough not to ruin what is otherwise a great game. The subtle interactions which you notice after playing it a few times create a great back and forth. It's also fairly accessible to the intermediate gamer who is looking for something deeper which can still finish in about an hour most of the time.
I have to say, if you haven't played it two player, or had it on your shelf when that 2 hour game was too long, you are missing out.